Electronic structure, first and second order physical properties of MPS₄: a theoretical study

We have calculated the electronic structure and physical properties of metal thiophosphate compounds InPS₄ and AlPS ₄by means of pseudopotential density functional theory (DFT) coupled with the modern theory of polarization. The targeted physical properties are first and second order optical properties as well as elastic, piezoelectric and electro-optic coefficients. Furthermore, population analysis is presented in order to evaluate the covalent-ionic character of the constituent bonds. The calculated elastic constants, refractive indices and second order optical coefficients of InPS₄ are in good agreement with experimental values. With the absence of any theoretical or experimental physical properties of AlPS₄, we predict that this compound has high piezoelectric coefficients with d₁₄ = − 73.82 pm/V, d₂₅ = − 10.96 pm/V and d₃₆ = 28.19 pm/V.