Electronic structure and optical properties of rhombohedral arsenic and their variations with the internal displacement parameter

The electronic band structure, density of states, and imaginary part of the dielectric function of rhombohedral As are calculated using the empirical pseudopotential method. The electronic density of states are calculated for five different values of the internal displacement parameter u, and the results are added, weighted by a Gaussian probability distribution in u. The resulting density of states is compared with that of rhombohedral and amorphous As. The imaginary part of the dielectric function of the distorted crystal is calculated using the above density of states along with the nondirect transition model and energy dependent matrix elements. A Kramers‐Kronig transformation is performed to obtain the real part of the dielectric function. Finally, the absorption coefficient of the distorted crystal is calculated. The optical constants of the distorted crystal are compared with those of rhombohedral and amorphous As.