Ab initio study of the structural, electronic, mechanical, dynamical, thermodynamic, linear and nonlinear optical properties of BeSiP2xAs2(1−x) quaternary alloys

Abstract

The quaternary alloys BeSiP2xAs2(1−x) with the noncentrosymmetric chalcopyrite structure are studied by means of ab initio density functional theory calculations. The calculations are shown the substitution of Asby P leads to the decrease of the volume of the unit cell and the increase of the energy band gap. Using the Zunger approach, the microscopic origins of the energy band gap bowing are examined in term of volume deformation bVD, charge exchange bCEand structural relaxation bS.The analysis of the total electron density distribution map is shown that the electrons flow from the As, Si and P atoms and accumulate into covalent bonds between the As and Si atoms and between the Si and P atoms. The effect of Pconcentration on the mechanical properties, phonon frequencies and Born effective charges Z∗ of these quaternary alloys are also investigated. The calculated results indicated that these quaternary alloys are mechanical and dynamically stable, have a brittleness character and can be regarded as elastically anisotropic materials. Moreover, the thermodynamic properties of these quaternary alloys including the heat capacity at constant volume CV, the Helmholtz free energy F and entropy S are calculated using the harmonic approximation based on the phonon density of states calculation. Finally, the nonlinear optical coefficient d36 of the quaternary alloys BeSiP2xAs2(1−x) is evaluated and the results confirm that these alloys are remarkable in the nonlinear optics. © 2021 Elsevier Ltd