Structural and Electronic Properties of BaSe and BaS: A First-Principles Study

Abstract

The structural and electronic properties of the alkaline-earth chalcogenides barium selenide (BaSe) and barium sulfide (BaS) are investigated from first principles within density functional theory (DFT), using the full-potential linearized augmented plane-wave plus local-orbitals (FP-LAPW+lo) method as implemented in the WIEN2k code. Total-energy calculations were performed for both the rock-salt (B1, Fm3m) and caesium-chloride-type (B2) phases, and the equilibrium lattice constant, bulk modulus, and its pressure derivative were extracted within the local density approximation (LDA) and the generalized gradient approximation (GGA); single-crystal elastic constants were also obtained. The computed lattice constants agree well with the available experimental and earlier theoretical values, with GGA systematically overestimating and LDA systematically underestimating the equilibrium volume relative to experiment, consistent with the well-documented behaviour of the two approximations. The calculated total density of states shows the valence band to be dominated by chalcogen p states hybridised with Ba 5d states, with a deeper, well-separated contribution from the Ba 5p semicore level. Band-structure calculations show that both BaSe and BaS are indirect-gap semiconductors, with the valence-band maximum at Γ and the conduction-band minimum near X; the Engel–Vosko GGA and the Tran–Blaha modified Becke–Johnson (mBJ) potential were used to improve the computed band gap beyond standard GGA. The results are compared throughout with the wider body of experimental and computational work on the barium and alkaline-earth chalcogenides, to which they are shown to be closely consistent, and provide a benchmark for the optical properties of the same two compounds reported in a companion paper.