First-principles study of rock-salt AgClxBr1−x alloys

We present first-principles calculations of the structural, electronic and thermodynamic properties of rock-salt AgClxBr1−x alloys by application of the full potential linearized augmented plane wave (FP-LAPW) method. We use both Perdew–Burke–Ernzerhof and Engel–Vosko generalized gradient approximations of the exchange-correlation energy that are based on the optimization of total energy and corresponding potential, respectively. The effect of composition on lattice constants, bulk modulus, cohesive energy, bond ionicity, band gap and effective mass was investigated. These parameters were found to depend nonlinearly on alloy composition x, except the lattice parameter, which follows Vegard's law. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers; we have concluded that the band gap energy bowing was mainly caused by the chemical charge-transfer effect, while the volume deformation and the structural relaxation contribute to the gap bowing parameter at smaller magnitude. On the other hand, the thermodynamic stability of AgClxBr1−x was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram.