Relativistic effects in the optical response of HgSe by time-dependent density functionals theory

We treat the dominant relativistic effects in the optical response properties of mercury selenide using time-dependent density functional theory (TDDFT). The scalar relativistic effects have been included within the zeroth-order regular approximation (ZORA) in both the ground-state DFT calculations and in the time-dependent response calculations. Within this approximation the HgSe crystal is found to be a semimetal. In a previous study [J Chem Phys 2001,114,1860] we have shown that TDDFT/ZORA can be applied successfully to narrow-gap semiconductors, such as indium antimonide, that become semimetallic within the local density approximation when scalar relativistic effects are included. Results are given for the band structure, the static dielectric constant epsilon (infinity), and the dielectric function epsilon(omega) of HgSe, and these results are compared with the similar ones for InSb. We find considerably improved results for the dielectric function of HgSe when relativistic effects are included. (C) 2001 John Wiley & Sons, Inc.