Computational study of adamantanes using floating basis functions

Abstract

Effects of the inclusion of a set of 6-311++Gfloating basis functions (FBFs) corresponding to the H, He, Li, Be, B, and C atoms, located at the center of molecular cage on the structural and bonding characteristics of the T d symmetric adamantane (A), tetrafluoroadamantane (TFA) and tetracyanoadamantane (TCA), and their anions are studied using B3LYP/(6-311++G+ FBF) method. Results show that neutral A, TFA, and TCA are stabilized most, by 3.22, 10.43, and 3.36 kJ/mol, when, respectively, Be, B, and B FBFs are used. Application of FBF results in much higher stabilizations for the negative ions of adamantanes. The highest stabilization energies for the negative ions A -, TFA -, and TCA - (36.49, 42.35, and 12.73 kJ/mol) are all obtained with the Li FBF. To detail effects of the FBF on the electronic structures of adamantanes, nuclei-independent chemical shift at the cage center is also calculated and analyzed. These results show explicitly that for accurate description of the molecular properties of cage compounds, such as adamantanes and diamondoids, the use of FBF is necessary. Application of the FBF affects also the vertical and adiabatic ionization potentials and electron affinities calculated for these cage species. © 2014 Springer Science+Business Media New York.