STRUCTURE OF MOLTEN MX–NdX<sub>3</sub> (M – Na, K, Rb, Cs; X – F, Cl) SALTS: AN <i>ab initio</i> STUDY

Abstract

The paper presents an ab initio study of neodymium containing clusters modeling the structure of corresponding molten salts. The relevance of such study is dictated by development of new methodologies and technologies for processing electronic and magnetic wastes, which are a valuable source of rare earth metals. In turn, quantum chemical calculations provide a powerful tool for investigation of structural features of model systems mimicking high temperature molten salts. In the present study, the simulations are performed within the Hartree–Fock and density functional theory approaches using the Firefly 8.20 software package. We propose a methodology for calculation of interaction energies in ternary systems including the neodymium complex, the outer-sphere cation shell, and the rest of the cluster. The interaction energies between the neodymium complex and other parts of a system are calculated. The dependence of interaction energies on the number of outer-sphere cations is investigated and the most stable “neodymium complex + outer-sphere shell” structures are determined. The calculated data are compared to direct spectroscopic investigations available in literature. The obtained interatomic Nd–X (X – F, Cl) distances coincide with experimentally deduced values. The computed Raman spectra for the 18MCl + M3NdCl6 (M – Na, K, Rb, Cs) model systems demonstrate a good agreement between calculated and experimentally observed positions of the most intense peak. Therefore, the chosen systems provide a reliable minimalistic model for quantum chemical investigations of molten salts structure.