Model calculations of the energy structure for the Cu6PS5Br crystals


Purpose. The compound Cu6PS5Br belongs to the large family of complex chalcohalides crystallizing in the argyrodite structures. The main peculiarity of copper-containing argyrodites is high solid-state ionic conductivity of the Cu+ ions, which makes it possible to use these argyrodite crystals as functional electronic materials. The main goal of the present works was to investigate the energetic structure of Сu6PS5Br crystals. At ambient temperature, the crystals under investigation are characterized by high symmetry: cubic syngony, space group F–43m, lattice parameter a = 9.708 Å. At temperature below 50 K, these crystal belong to monoclinic syngony, space group Cc, lattice parameters a = 11.8147 Å, b = 6.816 Å, c = 11.92 Å, β = 109.5°.
Methods. In the present study, the full energy and electronic spectra have been obtained in ab initio calculations for the superlattice of Cu6PS5Br containing 100 atomic positions 25 of which are occupied. The calculations have been performed by using the program ABINIT, within the framework of the Density Functional Theory (DFT) in Generalized Gradient Approximation (GGA).
Results. Zone structures have been calculated and presented for a series of model Сu6PS5Br phases

Keywords: argyrodites, crystal structure, superlattice, electronic spectrum, ab initio