First-principles DFT calculations of the electronic structure and optical properties of TlInGe2Se6, a prospective NLO material

Abstract

We present results of first-principles density functional theory (DFT) calculations of total density of states (DOS) and partial densities of states (PDOSs) of novel quaternary selenide TlInGe2Se6, a promising nonlinear optical (NLO) material. The calculations are performed employing the augmented plane wave + local orbitals (APW + lo) method as implemented in the WIEN2k package. The DOS and PDOSs curves reveal the significant hybridization between the electronic states of atoms composing the TlInGe2Se6 compound and forming its chemical bonds. The present DFT calculations indicate that the Se 4p states are the principal contributors to the valence band of TlInGe2Se6, making the main contributions to the top and upper portion of the band, while contributions of the Ge 4p and In 5s states dominate in its central portion and bottom, respectively. Furthermore, contributions of the unoccupied Ge 4s states dominate at the bottom of the conduction band of the compound under study. The calculated electronic bands along broad selected symmetry paths manifest that the conduction band minimum and the valence band maximum are positioned at the L point of the first Brillouin zone resulting in a direct band gap of the compound under consideration. The main optical constants, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity are studied for TlInGe2Se6 based on the APW + lo calculations.