Publication Date: 2024
Materials Chemistry and Physics (02540584)312
In this work, we delve into the investigation of mechanical and thermal properties of antiferromagnetic UX2 (X=P, As, Sb), which are structured in the unique anti-Cu2Sb-type tetragonal form. The study's principal findings revolve around the revelation of distinctive compressibility patterns and an observed preference for shear deformation in these compounds. These patterns are notably marked by a lower compressibility along the [100] direction than the [001] one, and the ease of shear deformation on the (100) plane compared to the (001) one. Intriguingly, our findings identify these compounds as residing on the brink of the brittle/ductile borderline as per Pugh's ratio and Poisson's ratio. Furthermore, the mechanical strength in these materials is significantly influenced by shear deformation, a fact indicated by the values of bulk and Young's modulus. Among the UX2 (X=P, As, Sb) compounds, our analysis of the Debye temperature singles out UP2 as an outstanding performer due to its higher Debye temperature. A noteworthy aspect of this study is the quicker propagation of longitudinal waves over transverse waves, as indicated by the wave velocity and anisotropy calculations. We bring forth an enriched understanding of the anisotropic behavior of these materials in terms of bulk modulus, Young's modulus, shear modulus, and Poisson's ratio. The predicted high melting temperatures of the UX2 (X=P, As, Sb) compounds, coupled with the computed heat capacities aligning well with existing experimental data, point towards their potential applicability in high-temperature settings. Collectively, our study not only validates the methodologies employed but also brings to light fascinating new insights into the mechanical and thermal properties of these compounds, deepening our understanding of the intricate interplay between their atomic constitution and physical properties. © 2023
Publication Date: 2024
Scientific Reports (20452322)14(1)
Ferroelectricity in metals has advanced since the initial discovery of nonmagnetic ferroelectric-like metal LiOsO 3 , anchored in the Anderson and Blount prediction. However, evaluating the spontaneous electric polarization (SEP) of this metal has been hindered by experimental and theoretical obstacles. The experimental challenge arises from difficulties in switching polarization using an external electric field, while the theoretical limitation lies in existing methods applicable only to nonmetals. Zabalo and Stengel (Phys Rev Lett 126:127601, 2021, https://doi.org/10.1103/PhysRevLett.126.127601) addressed the experimental obstacle by proposing flexoelectricity as an alternative for practical polarization switching in LiOsO 3 , which requires a critical bending radius similar to BaTiO 3 . In this study, we focus on resolving the theoretical obstacle by modifying the Berry phase and Wannier functions approaches within density functional theory plus modern theory of polarization. By employing these modifications, we calculate the SEP of LiOsO 3 , comparable to the polarization of BaTiO 3 . We validate our predictions using various ways. This study confirms the coexistence of ferroelectricity and metallicity in this new class of ferroelectric-like metals. Moreover, by addressing the theoretical limitation and providing new insights into polarization properties, our study complements the experimental flexoelectricity proposal and opens avenues for further exploration and manipulation of polarization characteristics. The developed approaches, incorporating modified Berry phase and Wannier function techniques, offer promising opportunities for studying and designing novel materials, including bio- and nano-ferroelectric-like metals. This study contributes to the advancement of ferroelectricity in metals and provides a foundation for future research in this exciting field. © 2024, The Author(s).
Mollabashi, L.,
Jalali asadabadi, S.,
Rudowicz, C.,
Acikgoz, M.,
Ghasemi-dorcheh, Z.,
Ebrahimi-jaberi, R.,
Jalali-asadabadi, M.,
Rahimi, S.,
Jalali-asadabadi, F. Publication Date: 2024
Physical Review B (24699950)110(5)
Studying magnetic properties of LiTmF4, a recognized insulating Van Vleck paramagnet, can hold promise for advancements in quantum computing, MRI, spintronics, material design, and potentially, single-photon technologies. This study may be pivotal due to challenges in simulating noncollinear magnetism using density functional theory (DFT), requiring more sophisticated spin configurations and time-consuming spin relaxations or embedded dynamical mean field theory. Instead, we utilize two distinct efficient and reliable schemes - ab initio DFT and a semiempirical superposition model, both integrated with crystal field (CF) theory (including Zeeman effect) and underpinned by statistical mechanics - to analyze noncollinear paramagnetic properties. At the core of this investigation is the S4 site symmetry of the Tm3+ ion, which admits several sets of six (seven) independent CF parameters (CFPs) under the reduced (complete) approach generated by suitable rotations of the coordinate system. By applying the Noether theorem, we show that these numerically distinct sets are physically equivalent. This is evidenced by computing the several conserved CFP quantities predicted by the Noether theorem, which exhibit notable coherence across different data sets. Using one of these equivalent sets of 7 CF parameters, as computed in [Phys. Rev. B 102, 045120 (2020)2469-995010.1103/PhysRevB.102.045120] under the complete approach, this study explores the theoretical analysis of multiplet splitting induced by the CF and the external magnetic field within the Tm3+ ion lattice in LiTmF4. We investigate the magnetic moment per ion and the temperature dependencies of magnetic susceptibility, utilizing a Hamiltonian, including the free ion, CF terms, and Zeeman interaction. The agreement of our findings with existing experimental data accentuates the efficacy of the proposed approach in reproducing magnetic properties in LiTmF4, providing a significant analytical tool for the analysis of EPR spectra in terms of the defined Zeeman g tensor. This research may stand as a pivotal guide in the accurate determination of magnetic properties, potentially influencing significant advancements in technology and materials science. © 2024 American Physical Society.
Publication Date: 2023
Physical Chemistry Chemical Physics (14639084)25(5)pp. 3986-4004
The rare-earth or 3d transition metal dopants in perovskites have potential to induce interesting features, thus opening opportunities for investigations and applications. Hence, understanding some features, i.e., defect structure, site of incorporation, valence state, and mechanism of charge compensation, in a wide range of temperature is crucial for their technological applications. A comprehensive understanding of the mechanism of structural changes in PbTiO3 doped with trivalent rare-earths is significant for their potential applications in photonics. To unravel the structural changes, we utilize the density functional theory (DFT) to optimize structural data, which then serve as input for the semiempirical superposition model (SPM) analysis of spectroscopic and magnetic properties of Gd3+-doped PbTiO3. We compute the formation energies of the doped compounds with and without O-vacancy to determine the stable composition. Analysis of the Bader electron charges computed using DFT plus quantum theory of atoms in molecules enables elucidating the effects of the Gd dopant and O-vacancy on the ionic and covalent bonds and, thereby, chemical stability of the compositions. To explain and corroborate the zero-field splitting parameters (ZFSPs) measured by EMR and the lattice parameter changes obtained from XRD, we employ SPM. The optimized structures obtained from ab initio computations for various structural models of Gd3+ doped PbTiO3 are utilized as input data for SPM calculations of ZFPs. This enables theoretical analysis of variations of ZFSPs from 5 to 780 K. The results were fine-tuned by matching with available experimental EMR data for Gd3+ probes in PbTiO3 nanoparticles. Modeling has been carried out considering several possible structural models and the role of an O-vacancy around Gd3+ centers. The results show that the two-fold modeling approach, combining DFT and SPM, provides a reliable description of experimental data. Comparative analysis indicates that the Ti-site is less favorable for being replaced by Gd3+ with/without O-vacancy. This analysis confirms the plausibility of the Pb2+ site for Gd3+ dopants and sheds light on the changes of crystal structure during the phase transitions occurring in PbTiO3 with decreasing temperature. © 2023 The Royal Society of Chemistry.
Publication Date: 2022
Physical Review B (24699950)106(11)
Antiferromagnetic (AFM) and high ferroelectric (FE) orderings coexist in the pristine BiFeO3. However, its performance is suppressed by complex FE switching originated from its R3c space group and high leakage current due to the volatile nature of Bi. We theoretically predict that the performance can be enhanced by (B,F) codoping. To this end, BiFeO3 and its Ba-doped, Bi1-xBaxFeO3-x/2, as well as (Ba,F) multidoped, Bi1-xBaxFeO3-xFx, are analyzed structurally, magnetically, optically, and electrically for the pure (doped) compound (compositions), where x=0.25. The analyses are performed in the framework of density functional theory accompanied by random phase approximation, Berry phase theory, and Hubbard model using PBE-GGA+U with Ueff=4(5)eV. Here, we predict that the tetragonal polar distortions of the co-doped compound with an AFM ordering lead to a nonzero spontaneous polarization. Hence, both the magnetic and electric polarizations coexist in the codoped composition. To assess the accuracy of the results, we calculate the spontaneous polarization for the pure BiFeO3 in both the R3c and P4mm symmetries and find the results in agreement with the available experimental and theoretical data. Furthermore, our dielectric functions for the pure case are found consistent with the experimental data. Moreover, absorption coefficient spectra, as calculated by GGA+U with Ueff=4eV and TB-mBJ with its self-consistently converged c=1.38 parameter, using Tauc method also reveal direct optical gaps of 2.66 and 2.80 eV, which agree with the corresponding experimental optical gap of 2.74 eV. To study the impacts of doping on the intrinsic ferroelectricity improvement of BiFeO3, we then calculate and analyze the optical absorption edges and loss functions for the pristine and doped compounds. By taking the band structure, partial densities of states, energy loss function, and parallel component of the imaginary part of the dielectric tensor, ℑ[ɛ∥], for the pure case into consideration simultaneously, the energies of the prominent peaks for ℑ[ɛ∥] spectra and their corresponding permitted absorption (emission) transitions are rigorously analyzed and determined. The analyses reveal that the sources of the prominent peaks occurred in ℑ[ɛ∥] mainly originate from the excitation states of the bound electrons of O 2s, O 2p, Bi 6s, Bi 6p, Fe 3d, and Fe 4s orbitals. Our results in most of the energy ranges show that the intrinsic ferroelectricity can be improved by the (Ba,F) codoping due to the reduction of the leakage current achieving from the calculated electric energy loss function. Further, the rhombohedral (R3c) is changed by the codoping to the tetragonal (P4mm) structure with more convenient symmetry for polarization switching. Hence, the system not only remains multiferroic after the codoping, but also its performance is enhanced. These evidences show that the codoping can play a key role for the applications of this multiferroic system in various devices. © 2022 American Physical Society.
Muhammad, Z.,
Liu, P.,
Ahmad, R.,
Jalali asadabadi, S.,
Franchini, C.,
Ahmad, I. Publication Date: 2022
AIP Advances (21583226)12(2)
The development of three-dimensional (3D) hybrid organic-inorganic perovskites has sparked much interest because of their rich light-harvesting capabilities in solar cells. However, the understanding of the electronic and optical properties, particularly the excitonic shifts upon structural phase transition with temperature in these materials, is not fully clear. Here, we report the accurate description of electronic and optical properties of mostly studied FAPbI3 across the cubic-tetragonal-hexagonal phases, using the relativistic GW method and Bethe-Salpeter Equation (BSE), including the spin-orbit coupling effects. Our GW calculations reveal that the bandgap values vary from 1.47 to 3.54 eV from the room temperature cubic phase to the low temperature hexagonal phase. Our optical analysis shows that excitonic peaks are blue-shifted, and exciton binding energies estimated by the model BSE approach increase from 74 to 567 meV going from the cubic to hexagonal phases. Our results may have important impacts on the practical uptake of hybrid perovskite based solar cells under different climatic conditions. © 2022 Author(s).
Publication Date: 2022
Scientific Reports (20452322)12(1)
We investigate temperature, pressure, and localization dependence of thermoelectric properties, phonon and de Haas–van Alphen (dHvA) frequencies of the anti-ferromagnetic (AFM) CeIn3 using density functional theory (DFT) and local, hybrid, and band correlated functionals. It is found that the maximum values of thermopower, power factor, and electronic figure of merit of this compound occur at low (high) temperatures provided that the 4f-Ce electrons are (not) localized enough. The maximum values of the thermopower, power factor, electronic figure of merit (conductivity parameters), and their related doping levels (do not) considerably depend on the localization degree and pressure. The effects of pressure on these parameters substantially depend on the degree of localization. The phonon frequencies are calculated to be real which shows that the crystal is dynamically stable. From the phonon band structure, the thermal conductivity is predicted to be homogeneous. This prediction is found consistent with the thermal conductivity components calculated along three Cartesian directions. In analogous to the thermoelectric properties, it is found that the dHvA frequencies also depend on both pressure and localization degree. To ensure that the phase transition at Néel temperature cannot remarkably affect the results, we verify the density of states (DOS) of the compound at the paramagnetic phase constructing a non-collinear magnetic structure where the angles of the spins are determined so that the resultant magnetic moment vanishes. The non-collinear results reveal that the DOS and whence the thermoelectric properties of the compound are not changed considerably by the phase transition. To validate the accuracy of the results, the total and partial DOSs are recalculated using DFT plus dynamical mean-field theory (DFT+DMFT). The DFT+DMFT DOSs, in agreement with the hybrid DOSs, predict the Kondo effect in this compound. © 2022, The Author(s).
Publication Date: 2020
Physical Review B (24699950)102(4)
Construction of an effective Hamiltonian including crystal field parameters (CFPs) by an accurate ab initio technique can provide a powerful approach for the measurements of tiny magnetic fields. Here, we first calculate the crystal field parameters (CFPs) of trivalent rare-earth magnetic ions R3+ in lithium rare-earth tetrafluorides LiRF4 (R = Tb, Dy, Ho, Er, Tm, and Yb) by the density functional theory plus the novel CFP scheme employing open-core treatment and Wannier functions. The behaviors of the real and imaginary parts of the CFPs are studied through the series of compounds. Then, by the calculated CFPs, we find the splittings of the energy levels of the +3 rare-earth ions by constructing an effective Hamiltonian for each case. The multiplet splittings of the +3 rare-earth ions are found to be consistent with those predicted by group theory and Hund's rules apart from some multiplet splitting of the Tm3+ and Dy3+ ions. For the former case, we have compared our theoretical results with the available empirical splittings of the multiplets. However, for the latter case due to the lack of experimental splittings, we have first empirically obtained the splittings of the multiplets employing the available experimental CFPs of the LiDyF3+:Dy3+ single crystal and then compared our empirical data with our ab initio theoretical predictions. The deviations of these two ions from the predictions of group theory and Hund's rules are found to be consistent with the experimental data. This validates the results reported and the reliability of the procedures performed to produce them. To simplify the effective Hamiltonian by reducing the number of CFPs, it is sometimes possible to use the D2d symmetry for some systems having S4 symmetry. However, by evaluating the matrix elements of the Stevens Hamiltonian term by term appeared in the Stevens CF Hamiltonian, it is shown that the actual S4 symmetry may provide more reliable results than its successor D2d symmetry for the systems under study having S4 symmetry. It can be predicted that this approach can be used for developing and improving sensitive magnetometer devices which, in turn, can play a key role in diverse areas. © 2020 American Physical Society.
Ali, L.,
Ahmad, M.,
Shafiq, M.,
Zeb, T.,
Ahmad, R.,
Maqbool m., M.,
Ahmad, I.,
Jalali asadabadi, S.,
Amin, B. Publication Date: 2020
Materials Today Communications (23524928)25
Perovskites CsSnX3 (X = Cl, Br and I) are promising for photovoltaic cells and other energy store devices, having high stability and less toxicity (lead free). The present work explored the structural, electronic and optical properties of these perovskites in different phases using generalized gradient approximation (GGA) and modified Becke-Johnson (TB-mBT) techniques. The structural properties of this system depend on temperature variation and selection of halogens, which changes the electronic and optical properties. The calculated structural parameters (lattice constants, bulk modulus, volume, bond length and bond angles) are in good agreement with the experimental values. The results presented in this article confirm that these compounds have direct band gaps, lie in the visible region (1.3–2.9 eV), hence they are more suitable candidates for optoelectronic devices. This study covers the lack of theoretical work concerned to these systems. © 2020 Elsevier Ltd
Publication Date: 2020
Journal of Alloys and Compounds (09258388)828
Here, we study the electron charge densities (ECDs) of two half-Heusler compounds, i.e. ZrCoBi and ZrRhBi, from topological point of view using the combination of DFT and quantum theory of atoms in molecules (DFT + QTAIM). We also investigate the structural properties and electronic structures of these compounds including DOSs, band structures and electron charge densities (ECDs) as well as the thermoelectric parameters including Seebeck coefficient and electrical conductivity. Furthermore, the effects of pressure on the properties of these compounds are investigated. The DFT + QTAIM calculations show that the compounds under study have similar numbers and types of critical points, but different bonds properties. The bonds of the Rh-case are more stable than those of the Co-case. Moreover, the ECD values at bonds of Rh-case are more than the Co-case. Imposing pressure affects some properties of the bonds in both cases, but does not change the numbers and types of their critical points. Based on our electronic structure calculations, Co-case has sharper valence DOSs near the Fermi level and larger band gap compared to the Rh-case. We have also observed flatter bands in the Co-case near the Fermi level compared to the Rh-case. In the anticipation of further study, the presented results may provide fundamental information which can pave the way for the study on the thermoelectric efficiencies of these interesting thermoelectric materials. In agreement with the electronic structure, our thermoelectric calculations show higher Seebeck coefficient and lower electrical conductivity for ZrCoBi than ZrRhBi. © 2020 Elsevier B.V.
Muhammad, Z.,
Liu, P.,
Ahmad, R.,
Jalali asadabadi, S.,
Franchini, C.,
Ahmad, I. Publication Date: 2020
Physical Chemistry Chemical Physics (14639084)22(21)pp. 11943-11955
We study the structural, electronic, and excitonic properties of mixed FAPb(I1−xBrx)30 ≤x≤ 1 alloys by first-principles density functional theory as well as quasiparticle GW and Bethe Salpeter equation (BSE) approaches with the inclusion of relativistic effects through spin orbit coupling. Our results show that the system volume decreases with increasing Br content. The quasiparticle band gaps vary from 1.47 eV for pure α-FAPbI3to 2.20 eV for Br-rich α-FAPbBr3and show stronger correlation with the structural changes. The optical property analysis reveals that the overall excitonic peaks are blue shifted with the Br fraction. Our results further reveal strong Br concentration dependence of the variation in the exciton binding energy (from 74 to 112 meV) and the carrier effective masses as well as the high frequency dielectric constants. These findings provide a way to tune the carrier transport properties of the material by doping, which could be utilized to improve the short circuit currents and power conversion efficiencies in multijunction solar cell devices. © the Owner Societies 2020.
Publication Date: 2019
Iranian Journal of Physics Research (16826957)19(1)pp. 37-48
In this paper, we study the structural and electronic properties of the cubic PbTiO3 compound by using the density functional theory. For the calculation of band structure and density of states, we use the modified Becke–Johnson exchange potential proposed by Tran and Blaha (TB-mBJ), including the relativistic spin-orbit coupling (SOC). The results obtained from TB-mBJ functional and SOC calculations show that the calculated band gap is 2.18 eV. IRelast computational package is very recently implemented into the WIEN2k code and can be used to calculate the elastic constants of the crystal structures, where IR stands for Iran. We calculate the elastic constants of this compound by the IRelast code using the PBE-GGA, PBEsol-GGA, LDA, BPW91 and Engel-Vosko functionals. Then, by these elastic constants, we obtain some other related physical quantities such as shear constant, bulk modulus, Young’s modulus and Poisson’s ratio. Furthermore, we calculate the ductility of the compound under question. The calculated ductility shows that our compound is formable and not fragile. The effect of pressure on the elastic constants shows that C11, C12 and C44 are increased as the pressure is raised inside the considered pressure interval. Furthermore, the longitudinal and transverse sound velocities are derived for the compound using its calculated elastic constants. The results, therefore, show that the sound velocities, like elastic constants, are increased as pressure is raised. © 2019, Isfahan University of Technology. All rights reserved.
Publication Date: 2019
Computational Condensed Matter (23522143)19
The electronic structure of γ-Al 2 O 3 in the presence of the Al and O defects is investigated within the density functional theory using the PBE-GGA and TB-mBJ schemes. The formation of the Al vacancy produces acceptor-like sublevels above the valence band maximum, consistent with the previous G 0 W 0 calculations. Furthermore, the formation of the oxygen vacancy generates donor-like sublevels below the conduction band minimum, which is consistent with experiment. The donor sublevels are predicted more accurately by TB-mBJ than PBE-GGA, as electron charge density is calculated to be larger at the O vacancy site by TB-mBJ within its optimized c-factor. © 2019 Elsevier B.V.
Publication Date: 2019
RSC Advances (20462069)9(62)pp. 36182-36197
Experimental evidences show that Ce-based compounds can be good candidates for thermoelectric applications due to their high thermoelectric efficiencies at low temperatures. However, thermoelectric properties have been studied less than the other properties for CeRhIn5, a technologically and fundamentally important compound. Thus, we comprehensively investigate the thermoelectric properties, including the Seebeck coefficient, electrical conductivity, electronic part of thermal conductivity, power factor and electronic figure of merit, by a combination of quantum mechanical density functional and semiclassical Boltzmann theories, including relativistic spin-orbit interactions using different exchange-correlation functionals at temperatures T ≤ 300 K for CeRhIn5 along its a and c crystalline axes. The temperature dependences of the thermoelectric quantities are investigated. Our results reveal a better Seebeck coefficient, electrical conductivity, power factor and thermoelectric efficiency at T ≪ 300, in agreement with various other Ce-based compounds, when a high degree of localization is considered for the 4f-Ce electrons. The Seebeck coefficient, power factor and thermoelectric efficiency are made more efficient near room temperature by decreasing the degree of localization for 4f-Ce electrons. Our results also show that the thermoelectric efficiency along the a crystalline axis is slightly better than that of the c axis. We also investigate the effects of hydrostatic pressure on the thermoelectric properties of the compound at low and high temperatures. The results show that the effects of imposing pressure strongly depend on the degree of localization considered for 4f-Ce electrons. © The Royal Society of Chemistry.
Publication Date: 2019
Computational Materials Science (09270256)164pp. 205-217
Recently, CeRhIn5 and CeCoIn5 with very different behaviors at ambient pressure were experimentally measured to exhibit comparable properties after applying pressure or doping impurity. Here, we study the electron charge densities (ECDs) of these compounds from topological point of view for the first time using the combination of DFT and quantum theory of atoms in molecules (DFT + QTAIM). We also investigate the electronic structures of these compounds including DOSs, band structures and electron charge densities (ECDs). The effects of applying pressure and degree of 4f-Ce electrons localization on properties of these compounds are also investigated, here. The DFT + QTAIM results in accordance with experiments reveal that at zero pressure these compounds have different TECD features and the features of CeRhIn5 can become similar to those of CeCoIn5, if in addition to applying pressure on CeRhIn5 the degree of 4f-electron localization is also properly reduced. Our results also confirm that chemical pressure by Sn doping in CeRhIn5 can make the features of its TECD somewhat similar to the pure CeCoIn5. © 2019 Elsevier B.V.
Publication Date: 2018
Iranian Journal of Physics Research (16826957)18(1)pp. 105-113
In this paper, the crystal field parameters (CFPs) have been calculated in the framework of the density functional theory using a novel theoretical approach proposed by Pavel Novák et al. and extracting the WANNIER functions from the Bloch eigenstates for the CeCl3 compound. Then, the calculated CFPs have been used in an effective atomic-like Hamiltonian, including the crystal field, 4f-4f correlation and spin-orbit coupling, and the splitted energy levels of Ce3+ ion by crystal field have been derived by diagonalization of the Hamiltonian. A hybridization parameter, , has been used to improve the results. The results are found to be in agreement with the experimental data. © 2018, Isfahan University of Technology. All rights reserved.
Publication Date: 2018
Journal of Electronic Materials (3615235)47(2)pp. 1045-1058
Cubic uranium compounds such as UX3 (X is a non-transition element of groups IIIA or IVA) exhibit highly diverse magnetic properties, including Pauli paramagnetism, spin fluctuation and anti-ferromagnetism. In the present paper, we explore the structural, electronic and magnetic properties as well as the hyperfine fields (HFFs) and electric field gradients (EFGs) with quadrupole coupling constant of UX3 (X = In, Tl, Pb) compounds using local density approximation, Perdew–Burke–Ernzerhof parametrization of generalized gradient approximation (PBE-GGA) including the Hubbard U parameter (GGA + U), a revised version of PBE-GGA that improves equilibrium properties of densely packed solids and their surfaces (PBEsol-GGA), and a hybrid functional (HF-PBEsol). The spin orbit-coupling calculations have been added to investigate the relativistic effect of electrons in these materials. The comparison between the experimental parameters and our calculated structural parameters we confirm the consistency and effectiveness of our theoretical tools. The computed magnetic moments show that magnetic moment increases from indium to lead in the UX3 family, and all these compounds are antiferromagnetic in nature. The EFGs and HFFs, as well as the quadrupole coupling constant of UX3 (X = In, Tl, Pb), are discussed in detail. These properties primarily originate from f and p states of uranium and post-transition sites. © 2017, The Minerals, Metals & Materials Society.
Publication Date: 2018
Materials Chemistry and Physics (02540584)212pp. 44-50
The structural, magnetic and elastic properties of orthorhombic phase of RAu2 compounds (R = La, Ce, Pr and Eu) are reported theoretically for the first time using full potential linearized augmented plane waves method within the density functional theory. The structural properties are investigated by treating the exchange and correlation energies with the generalized gradient approximation, PBEsol. Our computed lattice constants are found consistent with the reported experimental results. Our data reveal that they are stable in orthorhombic CeCu2 type structure. Their mechanical properties such as Young, Shear and bulk moduli, Poisson and anisotropic ratio, Cauchy pressure and Bo/G ratio are explored using the PBEsol to evaluate the importance of these compounds in various types of engineering applications. One of the striking features of their mechanical properties is their ductile nature. Magnetically all these intermetallics are antiferromagnetic. © 2018 Elsevier B.V.
Publication Date: 2018
Journal of Alloys and Compounds (09258388)735pp. 569-579
In this paper, we present the effectiveness of the IRelast package for the elastic constants (ECs) of crystals with different symmetries like Cubic, Hexagonal, Tetragonal, Orthorhombic, Rhombohedral and Monoclinic which are further used to investigate elastic and mechanical properties. The calculated results confirm the usefulness of the software by reproducing consistent experimental results. The reason for this competency is energy approach, where the calculated total ground state energy E(y,εij) is used for the calculations of the ECs. The software is also incorporated into the WIEN2K package. The purpose of the software is to provide a theoretical tool for researchers to calculate ECs of the unknown compounds and calculate ECs for experimentally measured ones for comparison purpose. © 2017 Elsevier B.V.
Publication Date: 2018
Journal of Physical Chemistry C (19327447)122(36)pp. 20589-20601
Nuclear magnetic resonance (NMR) parameters are calculated and analyzed in a series of titanate of alkaline earth perovskites to explore microscopic sources of their magnetic shieldings using a full-potential-based NMR scheme. In this method, there is no approximation to calculate the induced current density. The slope of the correlation between various approaches and available experimental data is successfully reproduced very close to the required ideal value (â1). Our NMR results are consistent with the experimental data and the available theoretical results calculated by the gauge-including projector augmented-wave (GIPAW) method. Moreover, we have predicted the chemical shifts of the compounds in which their experimental values have not been measured yet. Isotropic and anisotropic chemical shift parameters as well as associated asymmetries are analyzed. The analysis explores the relation between atomic and orbital characters of the valence and conduction bands wave functions as well as the 17O NMR shielding. Our results show that the NMR shielding varies by around 180 ppm through the materials under question. We, in agreement with the results reported on alkali fluorides, show that the variation of the NMR shielding in our investigated alkaline earth titanate perovskites is mostly related to the oxygen p-states. Furthermore, we show that the NMR chemical shifts strongly depend on the shape of the unoccupied titanium-d density of states (DOS) and alkaline-earth metals-d DOSs as well as their locations in the conduction region with respect to the Fermi level. It is also shown that the shielding calculated for the ordinary ice is less by 71.2 ppm than that derived for the water using TB-mBJ. © 2018 American Chemical Society.
Publication Date: 2018
Journal of Rare Earths (10020721)36(10)pp. 1106-1111
In this paper, we explored the structural, elastic and mechanical properties of the strongly correlated electron systems, intermetallic Ln-Au (Ln = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in cubic structure, using PF-LAPW method within the density functional theory. Structural properties of these intermetallics were investigated by treating the exchange-correlation potential with the GGA-PBE, GGA-PBEsol and GGA + U. The effectiveness of the U for the structural properties as compared to other methods confirms the strong correlated nature of these compounds and the calculated lattice constants endorse the divalency of Yb. The results demonstrate the stable cubic CsCl structure of these compounds. Bulk modulus, Young's modulus, shear modulus, B/G ratio, Cauchy pressure, Poisson's ratio, anisotropic ratio, Kleinman parameters and Lame's coefficients were studied using the PBEsol to evaluate their importance in various types of engineering applications. The most prominent features of these compounds are their ductility, very high melting points, resistance to corrosion, and anisotropic nature. © 2018 Chinese Society of Rare Earths
Publication Date: 2018
International Journal of Modern Physics B (02179792)32(2)
In this paper, we explore the structural, electronic, thermoelectric and elastic properties of intermetallic compounds ScTM (TM = Cu, Ag, Au and Pd) using density functional theory. The produced results show high values of Seebeck coefficients and electrical conductivity for these materials. High power factor for these materials at roomerature shows that these materials may be beneficial for lowerature thermoelectric devices and alternative energy sources. Furthermore, elastic properties of these compounds are also calculated, which are used to evaluate their mechanical properties. The Cauchy's pressure and B/G ratio figure out that these compounds are ductile in nature. The calculated results also predict that these compounds are stable against deforming force. © 2017 World Scientific Publishing Company.
Publication Date: 2018
Intermetallics (09669795)93pp. 77-84
In this paper, we explore the structural, magnetic, electronic specific heat, electric field gradient (EFG) as well as quadrupole coupling constant of NpPx3 (Px = Al, Ga, In) by using LDA, GGA, GGA + U and HF-PBEsol. The relativistic effects of electrons of the actinides are considered by spin-orbit coupling calculations. The comparison of the calculated structural parameters, magnetic moments and EFG of these materials satisfy the available experimental results. This consistency shows the effectiveness of our theoretical tools. The calculated EFG and quadrupole coupling constant value increase in NpPx3 from Al to In due to change of fermions. The EFG and quadrupole coupling constant in NpPx3 (Px = Al, Ga, In) is mainly originated from f-f and p-p contributions of Np atom and p-p contribution of Al, Ga and In atom. © 2017 Elsevier Ltd
Publication Date: 2017
Computational Materials Science (09270256)131pp. 308-314
In this article we communicate the spin-orbit interaction effects on the thermoelectric properties of alkaline-earth (A = Ca, Sr and Ba) based fully filled skutterudites ACo4Sb12. From the electronic structure calculations for ACo4Sb12 (A = Ca, Sr and Ba) it is understand that spin-orbit coupling take part in splitting of the states of the materials, however in case of BaCo4Sb12, with splitting, the maximum peak around the Fermi level also becomes sharper. This in turn affects the thermal performance of this material. Maximum peak value of Seebeck coefficient is significantly reduced for CaCo4Sb12 and SrCo4Sb12, however in case of BaCo4Sb12 Seebeck coefficient is increased significantly in the lower chemical potential region for n-type doping when spin-orbit coupling is added to the calculations. Furthermore there is also reduction in the electrical and electronic thermal conductivities for all compounds CaCo4Sb12, SrCo4Sb12 and BaCo4Sb12, due to spin-orbit interaction. Maximum zT's values obtained without spin-orbit interaction for CaCo4Sb12, SrCo4Sb12 and BaCo4Sb12 are 0.97, 0.95 and 0.64 whereas with the spin-orbit interaction maximum zT's values are 0.64, 0.59 and 0.69 respectively. © 2017 Elsevier B.V.
Khan, B.,
Yazdani-kachoei m., M.,
Rahnamaye aliabad h.a., H.R.,
Khan, I.,
Jalali asadabadi, S.,
Ahmad, I. Publication Date: 2017
Journal of Alloys and Compounds (09258388)694pp. 253-260
In this paper we explore the electronic nature and thermoelectric properties of filled skutterudites AFe(4)Sb(12) (A=Ca, Sr and Ba) by DFT and post-DFT techniques. The calculated results show that the filling of Ca, Sr, and Ba at the empty crystal sites enhances the thermoelectric performance of the host material. This increase is a consequence of the coupling between the guest and the host atoms, which affects the electronic density at different symmetry points that increases the density of states of the valence bands. The valence band edge is almost independent of the guest atoms, i.e., the s-bands of Ca, Sr and Ba have negligibly small contribution to the valence band edge. In these compounds, the maximum value of thermoelectric PF/tau of 42.43 x 10(14) mu W/cmK(2)s and 33.57 x 10(14) mu W/cmK(2)s for the n-type of SrAFe(4)Sb(12) in the spin-up and down states respectively. The striking feature of these compounds is their effectiveness at the low chemical potential values for the best thermoelectric performance. (C) 2016 Elsevier B.V. All rights reserved.
Publication Date: 2017
Intermetallics (09669795)91pp. 95-99
In this paper we explore the electronic charge distribution at different atomic sites in the rare-earth intermetallics RIn3 and RSn3 (R = La, Ce, Pr and Nd) using the analysis of the electric field gradients (EFGs) calculated by the FP-LAPW + lo method. The f-state in these compounds makes them strongly correlated systems, therefore the exchange and correlations are treated with GGA + U along with the GGA whereas GGA + SOC is also used to treat the relativistic effects. The calculated EFG values are consistent with the experimental results of the Mössbauer spectroscopy for LaSn3, CeSn3, CeIn3, PrSn3 and NdSn3 and therefore we expect that our calculated values for the remaining compounds will be also consistent with the experimental results. The anisotropy of the charge distribution in the vicinity of a nucleus causes EFG and therefore the orbitals contribution of EFG i.e., Vzzp−p, Vzzs−d, Vzzd−d, Vzzp−f and Vzzf−f are evaluated for nonmagnetic and AMF phases using GGA, GGA + U and GGA + SOC. © 2017 Elsevier Ltd
Publication Date: 2017
International Journal of Modern Physics B (02179792)31(32)
Spin-polarized density functional calculations are performed to study the correlation and spin-orbit coupling (SOC) effects in scandium intermetallic compounds viz. ScTM (TM=Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au) using FP-LAPW+lo method. The LDA, LDA+U and LDA+U+SOC exchange-correlation functionals are used to calculate the structural parameters and we found that the LDA+U results are consistent with the experiments. The electronic properties reveal that these compounds are metallic in nature. Correlations effects are determined using the U/W ratio and we found that ScCo, ScIr, ScPd, ScPt, ScCu and ScAg are highly correlated compounds, whereas ScRh, ScNi and ScAu are intermediately correlated compounds. Furthermore, stable magnetic phase for each compound is optimized, which reveals that ScCo, ScRh, ScPd, ScPt and ScCu are stable in ferromagnetic phase, ScIr, ScNi and ScAu are anti-ferromagnetic, whereas ScAg is a nonmagnetic material. © 2017 World Scientific Publishing Company.
Publication Date: 2017
Journal of Magnetism and Magnetic Materials (03048853)422pp. 458-463
In this article we explore the electronic and magnetic properties of RAu intermetallics (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) for the first time. These properties are calculated by using GGA, GGA+U and hybrid density functional theory (HF) approaches. Our calculations show that HF provides superior results, consistent to the experimentally reported data. The chemical bonding between rare-earth and gold atoms within these compounds are explained on the basis of spin dependent electronic clouds in different planes, which shows predominantly ionic and metallic nature between Au and R atoms. The Cohesive energies of RAu compounds show direct relation with the melting points. Spin-dependent electronic band structure demonstrates that all these compounds are metallic in nature. The magnetic studies show that HoAu and LuAu are stable in non-magnetic structure, PrAu is stable in ferromagnetic phase and CeAu, NdAu, SmAu, GdAu, TbAu, DyAu, ErAu, TmAu, YbAu are anti-ferromagnetic materials. © 2016 Elsevier B.V.
Publication Date: 2017
International Journal of Modern Physics B (02179792)31(21)
In this paper, we communicate a new type of Auger-free luminescence (AFL) compounds, alkali tin fluorides ASnF3 (A = Na, K, Rb and Cs). The luminescence in these compounds originates due to the electron transition from the top valence band (VB) of tin-s orbital to the outermost core levels of halogen, i.e., halogen-p orbital (s-p transitions). The AFL of these compounds is expected to be of L-type. Furthermore, the electronic band structures and optical properties such as dielectric functions, refractive index and energy loss function are also investigated using ab initio calculations. © 2017 World Scientific Publishing Company.
Publication Date: 2017
Physica B: Condensed Matter (09214526)526pp. 102-109
In this paper, we explore the structural and magnetic properties as well as electric field gradient (EFG), hyperfine field (HFF) and quadrupole coupling constant in actinide digallide AcGa2 (Ac = U, Np, Pu) using LDA, GGA, LDA+U, GGA+U and hybrid functional with Wu-Cohen Generalized Gradient approximation HF-WC. Relativistic effects of the electrons are considered by including spin-orbit coupling. The comparison of the calculated structural parameters and magnetic properties with the available experimental results confirms the consistency and hence effectiveness of our theoretical tools. The calculated magnetic moments demonstrate that UGa2 and NpGa2 are ferromagnetic while PuGa2 is antiferromagnetic in nature. The EFG of AcGa2 is reported for the first time. The HFF, EFG and quadrupole coupling constant in AcGa2 (Ac = U, Np, Pu) are mainly originated from f-f and p-p contributions of Ac atom and p-p contribution of Ga atom. © 2017 Elsevier B.V.
Publication Date: 2017
Physics Letters, Section A: General, Atomic and Solid State Physics (3759601)381(6)pp. 663-670
In this paper, we explore the structural, electronic and optical properties of ZnX and CdX (X = S, Se and Te) compounds in the two-dimensional (2D) graphene-like structure using the full potential augmented plane waves plus local orbitals (FP-APW+lo) method. Unlike their bulk phase, they are optically inactive because of their indirect band gap nature except CdS and ZnS. These two compounds maintain their direct band gap nature and hence are optically active. The static dielectric constants for these monolayers illustrate increasing trend with decrease in the band gap values. Furthermore, an acceptable description of electron transitions in these monolayers is accomplished according to the imaginary parts of the dielectric functions and absorption spectra in ZnS and CdS as examples of each group of CdX and ZnX. The results presented in this article revealed that ZnS and CdS in the 2D structure can be effectively used in optoelectronic devices such as solar cell materials and so forth. © 2016 Elsevier B.V.
Publication Date: 2017
JOURNAL OF PHYSICAL CHEMISTRY C (19327447)121(7)pp. 3978-3986
The electronic, magnetic, and optical properties of the Co2VAl (111) graphene-like (GL) monolayer as well as the (101) and (011) terminations have been calculated on the basis of the density functional theory (DFT) and FP-LAPW+lo method. The GL (111) Co2VAl has been grown in the (111)-crystallographic direction, leading to various and interesting physical properties compared to those of their considered directions. The films grown in the (101) and (011) directions have shown metallic behavior with low spin-polarization at the Fermi level, while the GL case has shown a perfect half-metallic behavior with an integer amount of magnetic moment (1.001 mu(B)) and 0.5 eV spin-flip gap. Thus, it can be a good candidate for spintronic applications. Although all of these thin films behave similarly in the ultraviolet region, the GL case appears to be different in the infrared and visible regions. The main plasmonic energies occur in the 12-13.8 eV energy range in the parallel (xx) and perpendicular (zz) directions. Our results show that the incident light cannot propagate in the visible region for all the considered monolayers.
Ahmad, M.,
Rehman, G.,
Ali, L.,
Shafiq m., ,
Iqbal r., ,
Ahmad, R.,
Khan, T.,
Jalali asadabadi, S.,
Maqbool m., M.,
Ahmad, I. Publication Date: 2017
Journal of Alloys and Compounds (09258388)705pp. 828-839
Organic-Inorganic perovskites CsPbX3(X = Cl, Br, I) are investigated for their potential ability and use as solar cells and energy storage materials, using density function theory, generalized gradient approximation and modified Becke-Johnson (TB-mBJ) exchange potential. Structural analysis shows that the lattice constant and unit cell volume varies when CsPbX3(X = Cl, Br, I) change from cubic phase to tetragonal and orthorhombic structures. The electronic properties show that CsPbCl3, CsPbBr3and CsPbI3all are semiconductor in with bandgap between 0.79 eV and 2.54 eV. It is also observed that the bandgap changes when the structure changes. Optical properties show that these materials have a good absorption ability of photons due to their narrow bandgaps. The real ε1(ω) and imaginary ε2(ω) parts of their dielectric functions show that CsPbCl3, CsPbBr3and CsPbI3also possess a great ability of retaining the energy it absorbs. These properties make them very suitable for solar cells and energy storage applications. These materials also behave as superluminescent material at high photon energy. © 2017 Elsevier B.V.
Rahnamaye aliabad h.a., H.R.,
Barzanuni z., ,
Sani, S.R.,
Ahmad, I.,
Jalali asadabadi, S.,
Vaezi h., ,
Dastras m., Publication Date: 2017
Journal of Alloys and Compounds (09258388)690pp. 942-952
We have investigated the structural, electronic, magnetic, phononic and thermoelectric properties of rare earth multiferroic manganite RMnO3(R = Gd and Tb) compounds by the density functional theory within the spin polarized GGA, LDA and mBJ + U + SOC. The full-potential linearized augmented plane wave and pseudopotential methods are used. The combined mBJ + U + SOC study indicates that the obtained results for the band gap are in close agreement with the experimental results. The Bader analysis show that the ionic nature of the Mn[sbnd]O bonds cause the large charge transfer from Mn to O atoms. Obtained band gaps are different for two spin channels therefore we have calculated the spin polarization dependence of transport properties. The directional thermoelectric study shows that these compounds are anisotropic. We have also presented the phononical properties such as Raman spectra and Born effective charges. © 2016 Elsevier B.V.
Bilal m., M.,
Saifullah, ,
Ahmad, I.,
Jalali asadabadi, S.,
Ahmad, R.,
Shafiq m., Publication Date: 2016
Solid State Communications (00381098)243pp. 28-35
In this paper, thermoelectric properties of carbon and nitrogen based twenty metallic antiperovskites MXY3 (M=Al, Ga, Ir, Mg, Pd, Pt, Rh; X=C, N; Y=Mn, Ni, Sc, Ti, Cr, Fe) using ab-initio density functional theory and post-DFT Boltzmann's techniques are investigated. The electronic properties of these compounds are also discussed. We find high values of Seebeck coefficient and small values of electronic thermal conductivity for AlCTi3, AlNSc3, AlCNi3, AlNTi3, GaCCr3 and MgCNi3 between -0.25 and 0.25 eV chemical potential. These results show high dimensionless figure of merit in metallic materials and therefore, we predict these materials can be potential candidates for low temperature thermoelectric applications. © 2016 Elsevier Ltd. All rights reserved.
Rehman, G.,
Shafiq m., ,
Saifullah, ,
Ahmad, R.,
Jalali asadabadi, S.,
Maqbool m., M.,
Khan, I.,
Rahnamaye aliabad h.a., H.R.,
Ahmad, I. Publication Date: 2016
Journal of Electronic Materials (03615235)45(7)pp. 3314-3323
The correct band gaps of semiconductors are highly desirable for their effective use in optoelectronic and other photonic devices. However, the experimental and theoretical results of the exact band gaps are quite challenging and sometimes tricky. In this article, we explore the electronic band structures of the highly desirable optical materials, III–V semiconductors. The main reason of the ineffectiveness of the theoretical band gaps of these compounds is their mixed bonding character, where large proportions of electrons reside outside atomic spheres in the intestinal regions, which are challenging for proper theoretical treatment. In this article, the band gaps of the compounds are revisited and successfully reproduced by properly treating the density of electrons using the recently developed non-regular Tran and Blaha’s modified Becke–Johnson (nTB-mBJ) approach. This study additionally suggests that this theoretical scheme could also be useful for the band gap engineering of the III–V semiconductors. Furthermore, the optical properties of these compounds are also calculated and compared with the experimental results. © 2016, The Minerals, Metals & Materials Society.
Publication Date: 2016
Bulletin of Materials Science (02504707)39(7)pp. 1861-1870
Ternary palladates CaPd3O4 and SrPd3O4 have been studied theoretically using density functional theory approach. The calculated structural properties are consistent with the experimental findings. Mechanical properties show that these compounds are elastically stable, anisotropic and ductile in nature. The electronic properties reveal that they are narrow band gap semiconductors with band gaps 0.12 and 0.10 eV, correspondingly. Both materials are optically active in the infrared ranges of the electromagnetic spectrum. Narrow band gap semiconductors are efficient thermoelectric (TE) materials; therefore, TE properties are also studied and discussed. Furthermore, DFT and post-DFT calculations confirm the paramagnetic nature of these compounds. © 2016 Indian Academy of Sciences.
Ahmad, S.,
Vaizie, H.,
Rahnamaye aliabad h.a., H.R.,
Ahmad, R.,
Khan, I.,
Ali, Z.,
Jalali asadabadi, S.,
Ahmad, I.,
Khan, A.A. Publication Date: 2016
International Journal of Modern Physics B (02179792)30(14)
This paper communicates the structural, electronic and optical properties of L-alanine, monofluoro and difluoro substituted alanines using density functional calculations. These compounds exist in orthorhombic crystal structure and the calculated structural parameters such as lattice constants, bond angles and bond lengths are in agreement with the experimental results. L-alanine is an indirect band gap insulator, while its fluorine substituted compounds (monofluoroalanine and difluoroalanine) are direct band gap insulators. The substitution causes reduction in the band gap and hence these optically tailored direct wide band gap materials have enhanced optical properties in the ultraviolet (UV) region of electromagnetic spectrum. Therefore, optical properties like dielectric function, refractive index, reflectivity and energy loss function are also investigated. These compounds have almost isotropic nature in the lower frequency range while at higher energies, they have a significant anisotropic nature. © 2016 World Scientific Publishing Company.
Publication Date: 2016
Scientific Reports (20452322)6
Two dramatic discrepancies between previous reliable experimental and ab initio DFT results are identified to occur at two different pressures in CeIn 3, as discussed through the paper. We physically discuss sources of the phenomena and indicate how to select an appropriate functional for a given pressure. We show that these discrepancies are due to the inaccuracy of the DFT + U scheme with arbitrary U eff and that hybrid functionals can provide better agreement with experimental data at zero pressure. The hybrid B3PW91 approach provides much better agreement with experimental data than the GGA + U. The DFT + U scheme proves to be rather unreliable since it yields completely unpredictable oscillations for the bulk modulus with increasing values of U eff. Our B3PW91 results show that the best lattice parameter (bulk modulus) is obtained using a larger value of α parameter, 0.4 (0.3 or 0.2), than that of usually considered for the AFM phase. We find that for hybrid functionals, the amount of non-local exchange must first be calibrated before conclusions are drawn. Therefore, we first systematically optimize the α parameter and using it investigate the magnetic and electronic properties of the system. We present a theoretical interpretation of the experimental results and reproduce them satisfactorily.
Publication Date: 2015
RSC Advances (20462069)5(47)pp. 37592-37602
In this paper, we explore the electric field gradients (EFGs) at 238U sites for antiferromagnetic UX2 (X = P, As, Sb, Bi) using LDA, LDA + U, GGA, GGA + U, and the exact exchange for correlated electrons schemes by considering the diagonalization of the spin-orbit coupling Hamiltonian in the space of the scalar relativistic eigenstates using the second-order variational procedure. The electronic structures and magnetic properties of the compounds are also investigated. It is found that the density functional theory approaches except exact exchange for correlated electrons are not successful in reproducing the experimental zero electric field gradient value in UBi2, even LDA + U and GGA + U within their default 4f density matrices by varying the U parameter in an energy interval of [0; 4 eV], though these techniques with no need to manually adopt their initial conditions (elements of the occupation matrix) are effective in the calculation of the nonzero electric field gradients for the other compounds. The exact exchange for correlated electrons has efficiently provided a null electric field gradient in UBi2 and nonzero electric field gradients for the other compounds by adjusting its dimensionless parameter α to 0.4. The physics of the null electric field gradient in UBi2 is revealed in this article and it is discussed that the source of the ignorable electric field gradient originates from the antiferromagnetic ordering of ↑↓ as compared to the long-range antiferromagnetic ordering of ↑↑↓↓ in the other compounds. Furthermore, our calculated magnetic moments for the uranium atoms in these compounds are consistent with the available experimentally measured values as compared to the severely underestimated theoretical results. © The Royal Society of Chemistry 2015.
Bilal m., M.,
Saifullah, ,
Shafiq m., ,
Khan b., ,
Rahnamaye aliabad h.a., H.R.,
Jalali asadabadi, S.,
Ahmad, R.,
Ahmad, I. Publication Date: 2015
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601)379(3)pp. 206-210
This letter communicates thermoelectric properties of antiperovskites SbNSr3 and BiNSr3, using ab-initio calculations. These compounds are identified as good transport materials for their narrow band gaps and dense electronic states near their Fermi levels. The peak values of Seebeck coefficient of 1590 and 1540 μV/K are observed for SbNSr3 and BiNSr3, respectively in the p-type regions, at room temperature. The figure of merit approaches unity for both materials, while their thermal conductivities increase and electrical conductivities decrease with temperature. These theoretical studies predict that these antiperovskites could be efficient materials for thermoelectric generators and need further experimental and theoretical studies. © 2014 Elsevier B.V. All rights reserved.
Publication Date: 2015
RSC Advances (20462069)5(30)pp. 23320-23325
In this article we explore the effects of dangling bonds and diameter on the electronic properties of the wurtzite InAs nanowires (NWs) using the density functional theory. The NWs are confined in the hexagonal supercell and are simulated in the [0001] direction. The calculations have been carried out by applying the periodic boundary conditions along the NW axis, i.e., z-Cartesian coordinate, providing enough vacuum to isolate the system from its neighbors. The optical properties of a material are directly related to the band-gap; therefore a relationship between the band-gap and diameter of the nanowires is obtained by using two models, where the band-gap for a larger diameter NW can be estimated. The results of these models are compared with each other and the effects of the dangling bonds on the band-gaps are also investigated. The band-gap of the nanowires decreases and the dangling bond ratio increases with the increase in the diameter of the nanowire, and hence we expect that for large diameter nanowires the band-gap will approach the band gap of the bulk material. An interesting feature of the shift in the band-gap from indirect to direct, i.e. optically inactive to active, is also observed in these NWs with the increase in the diameter. © The Royal Society of Chemistry 2015.
Shafiq m., ,
Arif, S.,
Ahmad, I.,
Jalali asadabadi, S.,
Maqbool m., M.,
Rahnamaye aliabad h.a., H.R. Publication Date: 2015
Journal of Alloys and Compounds (09258388)618pp. 292-298
In this article we communicate theoretical results of the mechanical properties of lanthanide monoxide LnO (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er and Yb) i.e., bulk modulus, shear modulus, Young's modulus, anisotropic ratio, Kleinman parameters, Poisson's ratio, Lame's coefficients, sound velocities for shear and longitudinal waves, and Debye temperature. Cauchy pressure and B/G ratio are also investigated to explore the ductile and brittle nature of these compounds. The calculations are performed with the density functional theory based full potential linearized augmented plane waves (FP-LAPW) method. The calculated results reveal that lanthanide based monoxides are mechanically stable and possess good resistive power against elastic deformations. Therefore, these mechanically stable materials can effectively be used for practical applications. The computed DOSs shows the metallic character of these compounds. Contour plots of the electron charge densities are also computed to reveal the nature of bonding in these compounds. © 2014 Elsevier B.V. All rights reserved.
Khan, B.,
Rahnamaye aliabad h.a., H.R.,
Saifullah, ,
Jalali asadabadi, S.,
Khan, I.,
Ahmad, I. Publication Date: 2015
Journal of Alloys and Compounds (09258388)647pp. 364-369
The electronic properties of complex binary skutterudites, MX3 (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. © 2015 Elsevier B.V. All rights reserved.
Publication Date: 2015
Journal Of Chemistry (20909071)2015
We present a review on the research developments on the theoretical electronic properties of the antiperovskite materials. The antiperovskite materials have perovskite type structure with the positions of cations and anions interchanged. The electronic structures are used to explain different physical properties of materials; therefore it is crucial to understand band structures and densities of states of materials for their effective use in technology. The theoretical results of the electronic structure of antiperovskites were discussed and compared with the available experimental results to measure the accuracy of the research done so far on these materials. The important physical properties of these compounds like magnetic properties and superconductivity are also highlighted. Nevertheless the thermoelectric properties of these materials are still unexplored except for a few reports which suggest that antiperovskite materials may be potential candidates for thermoelectric generators. © 2015 M. Bilal et al.
Publication Date: 2015
Journal of Magnetism and Magnetic Materials (03048853)381pp. 34-40
Ferromagnetic metallic inverse-perovskite (Eu3O)In is studied using hybrid functional theory (HF) in the frame work DFT. The calculated structural parameters and geometries of the material are calculated by different exchange correlation potentials and found that HF results are closed to the experiments. Electronic charge density explains the bond nature and polarization. The spin polarized electronic band profiles and density of states reveal the metallic nature of the compound. The Eu f-state splitting show that the valance bands are dominated mainly by f-[a2], f-[x(T1)], f-[y(T1)] and f-[z(T1)] states. The ground state magnetic phase of the compound is optimized. The optimum energy and magnetic susceptibility confirm the ferromagnetic nature of the compound. On the basis of different properties presented it is predicted that this compound is magnetoresistive material. © 2014 Published by Elsevier B.V.
Publication Date: 2015
RSC Advances (20462069)5(49)pp. 39416-39423
First principle studies of the cubic rare-earth intermetallics RIn3 and RSn3 (R = La, Ce, Pr, Nd) have been carried out within the framework of density functional theory using the full potential linearized augmented plane waves plus local orbital method (FP-LAPW + lo). The calculated structural parameters with different functionals are found to be consistent with the experimental results. The effect of the Hubbard potential on the density of states is discussed in detail. It is observed that the inclusion of spin-orbit coupling (SOC) causes degeneracies of the electronic band structures in the vicinity of the Fermi level of these compounds. Furthermore, the SOC effect enhances as one goes from La to Nd in a compound, which demonstrates the interesting nature of this effect in the periodic table. The elastic constants, bulk moduli, shear moduli, Young's moduli, anisotropy, Kleinman parameters, Poisson's ratios, sound velocities for shear and longitudinal waves, and Debye temperatures are calculated and discussed, which reveal that these compounds are ductile in nature. © The Royal Society of Chemistry 2015.
Papi h., ,
Jalali asadabadi, S.,
Nourmohammadi abadchi, A.,
Ahmad, I.,
Nematollahi, J.,
Yazdanmehr m., M. Publication Date: 2015
RSC Advances (20462069)5(68)pp. 55088-55099
The optical properties of pure γ-Al2O3 and in the presence of oxygen point defects are investigated by the density functional theory approach using the PBE-GGA and TB-mBJ-GGA schemes. The optical properties of the modeled imperfect crystal show closer agreement with the experimental results than the ideal crystal. The defects produce extra sharp bands and sub-bands, in the bandgap region. The TB-mBJ scheme provides better descriptions of the bandgaps and positions of the sub-bands compared to the experiments than the PBE-GGA scheme. The imaginary part of the dielectric function reveals that the sub-bands produced by the oxygen point defects act as trapping centers. The real part of the dielectric function and the index of refraction are also strongly affected by these defects and increase at 0 eV, decrease at 5 eV and remain constant at 80 eV with the defects. The intensities of the optical spectra are calculated by PBE-GGA to be higher than those of TB-mBJ. The higher intensities are mainly ascribed to the matrix elements of the linear momentum operator. © The Royal Society of Chemistry.
Khan, B.,
Rahnamaye aliabad h.a., H.R.,
Razghandi n., ,
Maqbool m., M.,
Jalali asadabadi, S.,
Ahmad, I. Publication Date: 2015
Computer Physics Communications (00104655)187pp. 1-7
HoMnO3 and its La and Y doped compounds Ho0.67La0.33MnO3 and Ho0.67Y 0.33MnO3 are investigated for their structural and thermoelectric transport properties. Small bandgaps of these compounds, as investigated by first principles calculations, make them suitable for application in thermoelectric devices. It is found that the bandgap of pure HoMnO3 increases with La and Y dopants. Thermoelectric parameters such as Seebeck coefficient, electric conductivity and thermal conductivity are calculated and their dependences on chemical potential are reported. Electrical conductivity is found to be of the order of 1020 1/m Ω s, and thermal conductivity of the order of 1015 W/mKs for all these alloys. HoMnO3 in pure form and in the presence of La and Y dopants is very suitable for thermoelectric devices and as alternative energy materials. © 2014 Elsevier B.V. All rights reserved.
Publication Date: 2015
Journal of Physics and Chemistry of Solids (00223697)86pp. 114-121
Abstract Osmium based perovskites AOsO3 (A=Ca, Sr and Ba) have been studied theoretically using density functional theory approach. These studies show that CaOsO3 and SrOsO3 are orthorhombic and BaOsO3 is cubic and are consistent with the experiments. The electronic band structures demonstrate that these compounds are metals. The magnetic studies verify the experimental observations at low temperature, where the spin effects are canceled by the orbitals. The stable magnetic phase optimizations and magnetic susceptibilities calculations by the post-DFT treatment confirm that CaOsO3 and SrOsO3 are weak ferromagnetic whereas BaOsO3 is a paramagnetic material. The directional magnetic study shows that these compounds are magnetically anisotropic, and reveals that the easy magnetization axis is [001] direction. © 2015 Elsevier Ltd.
Publication Date: 2015
Materials Chemistry and Physics (02540584)162pp. 308-315
Abstract In the present density functional studies, structural, mechanical and magneto-electronic properties of CaTaO3, SrTaO3 and BaTaO3 perovskites have been investigated. The calculated structural parameters by DFT and analytical methods are found consistent with the experiments. The analytically calculated tolerance factors of these compounds as well as their mechanical properties show that they are stable in the cubic phase. Furthermore elastic properties show that these materials are ductile in nature and confirm that BaTaO3 is harder than the rest compounds. The calculated spin dependent magneto-electronic properties reveal the paramagnetic metallic nature of these compounds. The electrical conductivity curve demonstrates significant conductivity above room temperature. On the basis of the presented properties it is expected that these compounds could be efficient electrode materials and need experimental investigations. © 2015 Elsevier B.V.
Publication Date: 2015
Electronic Materials Letters (17388090)11(3)pp. 466-480
In this paper we communicate the thermoelectric properties of carbon and nitrogen based metallic antiperovskites ANCa3 (A=Ge, Sn, Pb), BCFe3 (B=Al, Zn, Ga) and SnCD3 (D=Co and Fe) using the ab-initio calculations to explore efficient metallic thermoelectric materials. The consistency of the calculated results of SnCCo3 and SnCFe3 with the experimental results confirms the reliability of our theoretical calculations for the other investigated metallic antiperovskites. The results indicate that the thermopower of these materials can be enhanced by changing the chemical potential. The dimensionless figure of merit for the three nitrides approaches 0.96 at room temperature, which proves the usefulness of these materials in thermoelectric generators. Furthermore, the thermal conductivity is minimum at room temperature for chemical potential values between -0.25 μ(eV) and 0.25 μ(eV), and provides the maximum values of dimensionless figure of merit in this range. The striking feature of these studies is identifying a metallic compound, SnNCa3, with the highest value of Seebeck coefficient at room temperature out of all metals. The results anticipate that these materials could be efficient in thermoelectric generators; however, this needs experimental verification. © 2015, The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.
Publication Date: 2014
Computational Materials Science (09270256)85pp. 310-315
Structural, electronic and optical properties of antiperovskite compounds, SbNCa3 and BiNCa3, are studied by using the full-potential linearized augmented plane waves (FP-LAPW) method under the framework of density functional theory (DFT). The exchange-correlation potential is treated by local density approximation (LDA), generalized gradient approximation (GGA-PBEsol) and GGA developed by Engel and Vosko (EV-GGA). Furthermore, the modified Becke-Johnson (mBJ) potential is also applied to attain reliable results for the band gaps of these compounds. The calculated lattice constants are found consistent with the experimentally measured values and other theoretical results. The band profiles show that both of these materials are direct band gap semiconductors of about 1.1 eV gap. The direct band gap nature reveals that they may be effective in optical devices and therefore the optical properties of these compounds like the real and imaginary parts of dielectric function, refractive index and absorption coefficient are also calculated and discussed. © 2013 Elsevier B.V. All rights reserved.
Publication Date: 2014
Computational Materials Science (09270256)95pp. 592-599
In this paper we present details of our developed open source software, cubic-elastic, for the calculation of the elastic constants (ECs) of cubic crystals. The comparison of the calculated ECs for various types of cubic systems by this software with those from the other available softwares as well as experimentally measured results confirms that our code can predict reliable results. The success of our code originates from its use of single deformation. The other codes usually use rhombohedral strain (RS). RS leads to 3B0+4C44 expression. Hence, RS systematically adds error to the C44 through the bulk modulus calculations, and thereby may not be mathematically an appropriate approach. The total energy is accurately calculated by the WIEN2k within the highly accurate full-potential (linearized) augmented plane-waves plus local orbitals method. The ECs are calculated by the second-order derivatives of the fitted polynomials to the calculated total energies with respect to the elements of strain tensors at zero strains. We have presented the theoretical background and methodology of the cubic-elastic. We have validated the software by taking a variety of cubic samples into consideration and calculated their ECs. The zero bulk error calculations show that the results obtained from the cubic-elastic are in good agreement with the available experimental data and the previous theoretical results and predicts the sign of elastic constants correctly. The calculated Cauchy's pressure (C″) and Poisson's ratio (ν) of LaS predict that it is an ionic compound. This prediction is in agreement (disagreement) with the previous ionic (covalent) bonds prediction deduced from previous ν (C″). © 2014 Elsevier B.V. All rights reserved.
Ali, Z.,
Shafiq m., ,
Jalali asadabadi, S.,
Rahnamaye aliabad h.a., H.R.,
Khan, I.,
Ahmad, I. Publication Date: 2014
Computational Materials Science (09270256)81pp. 141-145
Density functional theory is used to investigate the structural, electronic and magnetic properties of the anti-perovskites NiNMn3 and ZnNMn3. The calculated structural parameters are found consistent with the experimental results. The spin-polarized calculations of the electronic properties show metallic nature of these compounds. Furthermore the magnetic phase for each compound is optimized, which reveals that both of these compounds prefer anti-ferromagnetic phase. The calculated effective magnetic moments are also found consistent with the experimental values. The studies presented in this paper confirm the magnetoresistive nature of these compounds. © 2013 Elsevier B.V. All rights reserved.
Publication Date: 2014
Journal of Applied Physics (10897550)116(10)
In this paper, the structural, elastic, and electronic properties of RIn3 and RSn3 (R = Sm, Eu, Gd) compounds have been investigated using the full potential linearized augmented plane wave plus local orbital method within the density functional theory. The structural properties are investigated using the LDA, GGA, and the band correlated LDA+U and GGA+U schemes. The lattice parameters are in good agreement with the available experimental results and the divalent state of Eu is also verified. The spin-orbit coupling is included in order to predict the correct electronic properties and splitting of 4f states of the rare earth elements is also incorporated. We calculated Bulk modulus, shear modulus, Young's modulus, anisotropic ratio, Kleinman parameters, Poisson's ratio, Lame's co-efficient, sound velocities for shear and longitudinal waves, and Debye temperature. We also predict the Cauchy pressure and B/G ratio in order to explore the ductile and brittle behaviors of these compounds. © 2014 AIP Publishing LLC.
Publication Date: 2013
Computational Materials Science (09270256)67pp. 151-155
The full potential linearized augmented plane wave (FP-LAPW) method within the frame work of the density functional theory is used to study BaTbO 3 in three different phases; cubic (space group pm-3m), tetragonal (I4/mcm) and orthorhombic (Ibmm). The calculated structural parameters and geometries are found in agreement with the experimental results. The spin polarized electronic band structures and densities of states for all the three phases demonstrate that BaTbO3 is insulator. The insulating nature of the material is consistent with the experiments and contradicts with the theoretical results of the metallic behavior and narrow band gap semiconductor. Furthermore, the calculated magnetic moment of Tb4+ is in close agreement with the experiments. This comprehensive theoretical study provides a realistic theoretical approach to understand BaTbO3 in its different phases. © 2011 Elsevier B.V. All rights reserved.
Ali, Z.,
Khan, I.,
Ahmad, I.,
Naeem s., ,
Rahnamaye aliabad h.a., H.R.,
Jalali asadabadi, S.,
Zhang d., Publication Date: 2013
Physica B: Condensed Matter (09214526)423pp. 16-20
The all electrons full potential linearized augmented plane waves (FP-LAPW) method with GGA+U is used to study SrTbO3 perovskite in cubic and orthorhombic phases. The structural parameters and ground state magnetic properties are found consistent with the experimental results. The electronic band structures and density of states demonstrate that SrTbO3 is a wide band gap semiconductor in both phases. The magnetic studies of the material show that the nature of the compound is G-type anti-ferromagnetic. The calculated magnetic moment of Tb+4 is found consistent with the experiments. Furthermore, the optical properties demonstrate that the optical gap of the material is 1.8 eV, which lies in the visible region of the electromagnetic spectrum and hence the compound can be used in optoelectronic devices. © 2013 Elsevier B.V. All rights reserved.
Khan, I.,
Ahmad, I.,
Rahnamaye aliabad h.a., H.R.,
Jalali asadabadi, S.,
Ali, Z.,
Maqbool m., M. Publication Date: 2013
Computational Materials Science (09270256)77pp. 145-152
Structural, electronic and optical properties of CdSxSe 1-x at various compositions (0 ≤ x ≤ 1) are investigated using full potential linearized augmented plane waves (FP-LAPWs) method. A structural phase transition from zinc-blende to wurtzite is observed in CdSxSe1-x with increase in S concentration. The theoretically calculated phase transition as well as structural parameters like ground state energies, lattice constants and bulk moduli is in agreement with the experimental results. As CdSxSe1-x compound belongs to strongly correlated systems, therefore modified Becke-Johnson potential is used to calculate band gap energies and optical properties of the compound. The direct band gap nature of the material varies in the visible part of the spectral region for the whole range of S. The optical properties, like dielectric functions, refractive index, birefringence and energy loss function, are also calculated. The hexagonal wurtzite CdSSe is anisotropic and the calculated birefringence is found to be positive in the lower energy levels and negative in the higher levels. © 2013 Elsevier B.V. All rights reserved.
Publication Date: 2013
Journal of Physics and Chemistry of Solids (00223697)74(2)pp. 181-188
The electronic and optical properties of BeSxSe1-x, BeSxTe1-x and BeSexTe1-x, (0≤x≤1) are studied using the highly accurate modified Beck and Johnson (mBJ) potential. The binary Be-chalcogenides are wide and indirect band gap semiconductors and hence they are not efficient materials for optoelectronics. In order to modify them into optically active materials, the anion chalcogen atoms are partially replaced by other chalcogen atoms like BeS xSe1-x, BeSxTe1-x and BeSe xTe1-x (0≤x≤1). The modified ternary compounds are of direct band gap nature and hence they are optically active. Some of these direct band gap materials are lattice matched with silicon and can possibly replace Si in semiconductor devices. Keeping in view the importance of these materials in optoelectronics, the optical properties of BeSxSe 1-x, BeSxTe1-x and BeSexTe 1-x in the full composition range are investigated. It is found that these materials are transparent in the IR, visible and near UV spectral regions. The alloys for the most of the concentrations have band gaps larger than 3 eV, so it is expected that they may be efficient materials for blue, green and UV light emitting diodes. © 2012 Elsevier Ltd. All rights reserved.
Publication Date: 2012
Iranian Journal of Physics Research (16826957)11(4)pp. 62-62
This study investigated the electronic properties of antiferromagnetic UBi2 metal by using ab initio calculations based on the density functional theory (DFT), employing the augmented plane waves plus local orbital method. We used the exact exchange for correlated electrons (EECE) method to calculate the exchange-correlation energy under a variety of hybrid functionals. Electric field gradients (EFGs) at the uranium site in UBi2 compound were calculated and compared with the experiment. The EFGs were predicted experimentally at the U site to be very small in this compound. The EFG calculated by the EECE functional are in agreement with the experiment. The densities of states (DOSs) show that 5f U orbital is hybrided with the other orbitals. The plotted Fermi surfaces show that there are two kinds of charges on Fermi surface of this compound.
Publication Date: 2012
Nanoscale Research Letters (1556276X)7
γ-Al2O3 is a porous metal oxide and described as a defective spinel with some cationic vacancies. In this work, we calculate the electronic density of states and band structure for the bulk of this material. The calculations are performed within the density functional theory using the full potential augmented plan waves plus local orbital method, as embodied in the WIEN2k code. We show that the modified Becke-Johnson exchange potential, as a semilocal method, can predict the bandgap in better agreement with the experiment even compared to the accurate but much more expensive green function method. Moreover, our electronic structure analysis indicates that the character of the valence band maximum mainly originates from the p orbital of those oxygen atoms that are close to the vacancy. The charge density results show that the polarization of the oxygen electron cloud is directed toward aluminum cations, which cause Al and O atoms to be tightly connected by a strong dipole bond. © 2012 Yazanmehr et al.; licensee Springer.
Publication Date: 2012
Nanoscale Research Letters (1556276X)7(1)pp. 1-7
The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure. Different excitation wavelengths are used to identify most of the details of the subband states. The films are produced under different anodizing conditions to optimize their emission in the visible range. Scanning electron microscopy investigations confirm pore formation in the produced layers. Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing. © 2012 Nourmohammadi et al.; licensee Springer.
Publication Date: 2012
Thin Solid Films (00406090)520(7)pp. 2901-2908
Structural, electronic and magnetic properties were calculated for the optimized α-U/W(110) thin films (TFs) within the density functional theory. Our optimization for 1U/7W(110) shows that the U-W vertical interlayer spacing (ILS) is expanded by 14.0% compared to our calculated bulk W-W ILS. The spin and orbital magnetic moments (MMs) per U atom were found to be enhanced from zero for the bulk of α-U to 1.4 μ B and - 0.4 μ B at the interface of the 1U/7W(110), respectively. Inversely, our result for 3U/7W(110) TFs shows that the surface U-U ILS is contracted by 15.7% compared to our obtained bulk U-U spacing. The enhanced spin and orbital MMs in the 1U/7W(110) were then found to be suppressed in 3U/7W(110) to their ignorable bulk values. The calculated density of states (DOS) corroborates the enhancement and suppression of the MMs and shows that the total DOS, in agreement with experiment, is dominated in the vicinity of Fermi level by the 5f U states. Proximity and mismatch effects of the nonmagnetic W(110) substrate were assessed and found to be important for this system. © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2011
Iranian Journal of Physics Research (16826957)10(4)pp. 301-308
Single and double equilibrium bond lengths of the fcc-C60 crystal were calculated in the absence and presence of theendohedral C atom as an impurity doped into each C60 cluster, i.e., fcc-C@C60, by means of fully-relaxed self-consistent calculations within the density functtional theory (DFT) employing the full potential-augmented plane waves plus local orbital (FP-APW+lo) method. The result shows that the single and double bond lengths were decreased for the doped case of fcc-C@C60 when compared with the pure fcc-C60. The reduction in the bond lengths by the carbon impurity doping is attributed to the bond alternation effect and reduction of the symmetry in the C60 molecule. The result shows that the impurity injection gives rise to change in the electron charge distribution and as a result to change in electronic properties.
Publication Date: 2010
Journal of Applied Physics (10897550)108(7)
It is well known that the surface of nonmagnetic α-Ce is magnetically ordered, i.e., γ-like. One then might conjecture, in agreement with previous theoretical predictions, that the γ-Ce may also exhibit at its surfaces even more strongly enhanced γ -like magnetic ordering. Nonetheless, our result shows that the (111)-surfaces of magnetic γ-Ce are neither spin nor orbitally polarized, i.e., α -like. Therefore, we predict, in contrast to the nonmagnetic α -phase which tends to produce magnetically ordered γ -like thin layers at its free surfaces, the magnetic γ -phase has a tendency to form α -like dead layers. This study, which explains the suppressed (promoted) surface magnetic moments of γ-Ce (α-Ce), shows that how nanoscale can reverse physical properties by going from bulk to the surface in isostructural α - and γ -phases of cerium. We predict using our freestanding surface results that a typical unreactive and nondiffusive substrate can dramatically influence the magnetic surface of cerium thin films in contrast to most of the uncorrelated thin films and strongly correlated transition metals. Our result implies that magnetic surface moments of α-Ce (111) can be suddenly disappeared by increasing lattice mismatch at the interface of a typical unreactive and nondiffusive substrate with cerium overlayers. © 2010 American Institute of Physics.
Publication Date: 2009
Computational Materials Science (09270256)47(2)pp. 584-592
The Pb/Si(1 1 1) thin films were simulated within the density functional theory (DFT). The well-known Perdew-Burke-Ernzerhof (PBE) version of the generalized gradient approximation (GGA) and its recent nonempirical successor Wu-Cohen (WC) issue were used to estimate the exchange-correlation functional. Lattice parameters were calculated for bulk of the Pb and Si compounds to obtain more reliable lattice mismatch at the interface to be consistent with our used full-potential method of calculations. The WC-GGA result predicts the lattice constants of the Pb and Si compounds better than the GGA when compared with experiment. We have found that the spin-orbit coupling (SOC) does not significantly influence the results. Our finding is in agreement with the recent observation of the Rashba-type spin-orbit splitting of quantum well states in ultrathin Pb/Si(1 1 1) films. Our result shows, in agreement with experiment, that the top site (T1) is the most stable phase. A combination of tight σ and feeble π bonds has been found at the interface, which results in a covalent Pb-Si bond. Our calculated electric field gradient (EFG) predicts quantum size effects (QSE) with respect to the number of deposited Pb layers on the Si substrate. The QSE prediction shows that the EFG dramatically drops on going from first to second layer. The EFG calculation shows that this system is not an ideal paradigm to freestanding films. © 2009 Elsevier B.V. All rights reserved.
Publication Date: 2007
Physical Review B - Condensed Matter and Materials Physics (10980121)75(20)
Electric field gradients (EFGs) were calculated for the Ce In3 compound at both In and Ce sites. The calculations were performed within the density functional theory (DFT) using the augmented plane waves plus local orbital (APW+lo) method employing the so-called LDA+U scheme. The Ce In3 compound was treated as nonmagnetic, ferromagnetic, and antiferromagnetic cases. Our result shows that the calculated EFGs are dominated at the Ce site by the Ce-4f states. An approximately linear relation is intuited between the main component of the EFGs and the total density of states (DOS) at Fermi level. The EFGs from our LDA+U calculations are in better agreement with experiment than previous EFG results, where appropriate correlations had not been taken into account among 4f -electrons. Our result indicates that correlations among 4f -electrons play an important role in this compound and must be taken into account. © 2007 The American Physical Society.
Publication Date: 2004
Physica B: Condensed Matter (09214526)349(1-4)pp. 76-83
We investigated the effect of spin polarization on the structural properties and the electric field gradient (EFG) on Sn, In, and Cd impurities in RSn3 (R = Sm, Eu, Gd) and RIn3 (R = Tm, Yb, Lu) compounds. The calculations were performed self-consistently using the scalar-relativistic full potential linearized augmented plane wave method. The local density approximations and generalized gradient approximation (GGA) without spin polarization and with spin polarization (GGA+SP) to density functional theory were applied. In addition to that we performed some calculations within open core treatment (GGA+open core). It is clearly seen that GGA+SP is successful in predicting the larger lattice parameter and the dramatic drop of EFG for R = (Eu, Yb) relative to other rare-earth compounds. © 2004 Published by Elsevier B.V.
Publication Date: 2002
Physical Review B - Condensed Matter and Materials Physics (10980121)66(19)pp. 1-10
In (formula presented) and (formula presented) the rare earth (R) is trivalent, except for Eu and Yb, which are divalent. This was experimentally determined in 1977 by perturbed angular correlation measurements of the electric-field gradient on a (formula presented) impurity. At that time, the data were interpreted using a point charge model, which is now known to be unphysical and unreliable. This makes the valency determination potentially questionable. We revisit these data, and analyze them using ab initio calculations of the electric-field gradient. From these calculations, the physical mechanism that is responsible for the influence of the valency on the electric-field gradient is derived. A generally applicable scheme to interpret electric-field gradients is used, which in a transparent way correlates the size of the field gradient with chemical properties of the system. © 2002 The American Physical Society.
Publication Date: 2002
Physical Review B - Condensed Matter and Materials Physics (10980121)66(19)pp. 1951031-19510310
In RIn3 and RSn3 the rare earth (R) is trivalent, except for Eu and Yb, which are divalent. This was experimentally determined in 1977 by perturbed angular correlation measurements of the electric-field gradient on a 111Cd impurity. At that time, the data were interpreted using a point charge model, which is now known to be unphysical and unreliable. This makes the valency determination potentially questionable. We revisit these data, and analyze them using ab initio calculations of the electric-field gradient. From these calculations, the physical mechanism that is responsible for the influence of the valency on the electric-field gradient is derived. A generally applicable scheme to interpret electric-field gradients is used, which in a transparent way correlates the size of the field gradient with chemical properties of system.
