Towards a deeper understanding of physical and chemical properties of Ag2Hg□I4 and Cu2Hg□I4 defective crystals, from first principles calculations

Pressure effect on the Ag2Hg□I4 and Cu2Hg□I4 defective compounds is studied from the point of view of the density functional theory. The pressure-induced changes chemical coordination and bonding nature were attributed to an order–disorder phase transition in the cation sublattice. Advantages of the analysis of the topology of the electron localization function (ELF) in the characterization of the chemical bonding change are illustrated. The ELF gives deep insight for interpreting the bonding behavior of the metallic defect rock salt structure while pressure is increasing. The calculated energy band gaps from mBJ(EV-GGA) potentials are used to predict electro-optic properties of the β phase of the Ag2Hg□I4 and Cu2Hg□I4 compounds. We make use of interband and intraband resonances contributions to analyze linear and nonlinear susceptibilities. The analysis makes semiconducting phase of the investigated compounds as promising for an intensive optoelectronic application.