First-principles molecular dynamics simulations on the local structure and thermo-kinetic properties of molten magnesium chloride

Abstract

MgCl2 is a salt of considerable interest for the concentrating solar thermal power (CSP) system with advantages of high operating temperature and low cost. While the value of first-principles molecular dynamics (FPMD) simulations in investigating molten salt has been illustrated in many studies, there have been very few studies on molten MgCl2 from a first-principles method. In this work, FPMD simulations are employed to investigate the local coordination structure, as well as its structural dynamics, and thermo-kinetic properties of molten MgCl2. The basic thermo-kinetic properties of density, diffusivity, and ion conductivity are calculated for pure MgCl2 at multiple temperatures. The partial radial distribution function, partial structure factor, probability distribution of coordination numbers, and bond angle distribution are also derived from FPMD simulations. FPMD simulations are found to give satisfactory structural and transport characteristics compared with experiments. This study shows that the four-fold coordinated Mg2+ cations exist in pure MgCl2 and the Mg2+ first coordination shell has more octahedral geometry with anion vacancies. In conclusion, this work shows that FPMD simulations provide an effective method for exploring molten salts, which can be used in future research on Mg-based salts.