Cohesion energy simulation of inorganic layered alkaline-earth fluorohalides

Abstract

Within the framework of an interionic potential model, electrostatic and repulsive energies, lattice self-potentials for distinct ions, and the Madelung constant were calculated for several technologically important layered alkaline-earth fluorohalide scintillators belonging to the matlockite family and crystallizing with the PbFCl-type structure. The Coulombic term was computed using the conventional Ewald method, where the formulas were adjusted to optimize the computer calculation, and the overlap repulsive term was computed by means of an empirical approach based on the compressible ionic theory. The dispersive contribution was quantified using well-known formulations, and the polarization contribution was determined purely by geometric considerations based on both the size and anisotropic coordination of the highly polarizable halogen atom. In general, the obtained results were found to be in close agreement with the available data, except for the contribution of short-range interactions in the lattice. A quantitative explanation has been proposed to elucidate the differences detected. It was pointed out that the structural stability of these lamellar structures can be understood in terms of the anisotropic coordination of halogen anions, especially the high coordination of metal cations combined with their sizes. Our calculations led to an accurate evaluation of the cohesive energy, which, to the best of our knowledge, has never been measured before. Finally, the corresponding results will be useful for a better understanding of the chemical bonds and structural behavior of PbFCl-type compounds at high pressures.