Experimental and theoretical investigation of the electronic structure and optical properties of TlHgCl3 single crystal

Abstract

We have synthesized single crystals of TlHgCl3, which posses an orthorhombic symmetry, space group Pnma, with lattice constants a=9.1601(4)Å, b=4.3548(2)Å and c=14.0396(5)Å. The measurements of the optical absorption of TlHgCl3 are performed on parallel-plate samples with polished optical quality surfaces of d=0.03mm. The band gap is estimated to be 2.74eV from the position of fundamental absorption edge at α=200cm−1. We have used our measured crystallographic data of TlHgCl3 as input data for calculating the electronic band structure, density of states, electronic charge density and the optical properties. The all-electron full potential linearized augmented plane wave plus local orbital (FP-L(APW+lo)) method is used. Calculations are performed with three types of exchange correlations; local density approximation (LDA), general gradient approximation (PBE-GGA) and the recently modified Becke-Johnson potential (mBJ). The PBE-GGA is used to optimize the atomic positions by minimization of the forces (1mRy/au) acting on the atoms. The obtained values of the band gap from various exchange correlations are 2.39eV (LDA), 2.55eV (PBE-GGA) and 2.69eV (mBJ). It is clear that mBJ succeeded by a large amount in bringing the calculated energy gap closer to the experimental one. The calculated electronic band structure exhibits that the conduction band minimum and the valence band maximum are located at Z point of the BZ, resulting in a direct band gap. The calculated density of states provides information about the hybridization between the states and the bonding nature. The electronic charge density show that Hg and Cl atoms form partial ionic/covalent bonding between Cl–Hg–Cl. Furthermore, for a deep insight into the electronic structure we have investigated the optical properties.