Calculations within DFT framework of the electronic and optical properties of quaternary sulfide Tl2PbSiS4, a prospective optoelectronic semiconductor

Abstract

We report results of computation within framework of density functional theory (DFT) of the electronic band-structure of quaternary thallium lead silicon sulfide, Tl2PbSiS4. Especially, we employ different approaches for exchange correlation (XC) potential to find the best fit of the theoretical total density of states (TDOS) curve to the experimental valence band (VB) spectrum as elucidated employing the method of X-ray photoelectron spectroscopy (XPS). The present findings indicate that the best fit of the experimental and theoretical data regarding the shape of the VB XPS spectrum and TDOS is derived when employing in the computation procedure for XC potential the modified Becke-Johnson (MBJ) approach, which includes also spin-orbit (SO) effect and Hubbard parameter U for strongly correlated electrons of d symmetry (MBJ + U + SO technique). Based on these findings, we have performed computation of the electronic band-structure and primary optical constants of Tl2PbSiS4. The MBJ + U + SO calculations present that the main contributors at the top of the VB in this quaternary sulfide are S 3p states, the central portion is prevailed by the input of S 3p and Si 3p states, while the bottom is determined by contributions of the electronic states of s symmetry associated with lead and silicon.