Specific features of electronic structure and linear optical properties of some pseudocubic compounds

We have performed ab initio theoretical calculations of the electronic structure and the linear optical susceptibilities for the pseudocubic compounds X3As4 (X = C, Si, Ge, and Sn) using two approximations for the exchange correlation (XC) potentials: the generalized gradient approximation (GGA) by Perdew, Burke and Ernzerhof (PBE) and Engel–Vosko generalized gradient approximation (EVGGA) scheme. Our calculations show that the C3As4 compound is metallic with density of states at the Fermi energy EF, N(EF) of 3.808 and 1.904 states/Ry-cell or a bare electronic specific heat coefficient of 0.660 and 0.330 mJ/mole-K2 for GGA and EVGGA, respectively. The overlapping between the valence and conduction bands is strong resulting in metallic behavior. The EVGGA try to reduce the overlapping around EF by around the half value. Also we notice that the effect of EVGGA cause increase/reduce the peaks high and to make noticeable anisotropy between ε2II(ω) and ε2⊥(ω) for Ge3As4 compound. We found that X-s/p and As-s/p/d states are controlled the overlapping around EF. The effect of using EVGGA over GGA on the density of states and linear optical properties is very pronounced. Detail comparison of our calculated partial density of states and the frequency dependent dielectric function with the available calculations were made. We hope that future experiments will help in deciding which calculation is better.