Thermodynamic description of the K, Be//F, Cl salt system with first-principles calculations

Abstract Reciprocal molten halides are a distinctive class of high-temperature ionic liquids used as thermal and electrolytic media in the respective fields of MSR (molten salt nuclear reactor) and metallurgy. Strong S hort- R ange O rdering (SRO) from both the first-nearest (cation-anion) and second-nearest (cation-cation and anion-anion) neighbors defy accurate theoretical simulations of their physical and chemical properties and hence impede quantitative designs of optimum media applicable to industrial sectors. Based upon the M odified Q uasichemical M odel in the Q uadruplet A pproximation (MQMQA) coupled with the M ulti- S tate M odel (MSM), we developed a model (K+, BeIV2+, Be24+//F−, Cl−) to describe the thermodynamic behavior of the complex reciprocal K, Be//F, Cl liquid, where various types of SRO were evidenced by theoretical and experimental observations. This combinatorial method can quantitatively generate various sorts of quadruplets, thus providing structural entities to build other thermo-physical models. The thermodynamic properties of solid salts were also investigated to be able to calculate the entire reciprocal phase diagram. A vast amount of DFT ( D ensity F unctional T heory)-based first-principles predictions was performed based on various combinations of Pseudopotentials and Exchange-Correlation Functionals, SQS ( s pecial q uasi-random s tructure) models of solid solutions and data-mining screened crystal structures of double salts. The calculations are in satisfactory agreement with the available experimental data, thus showing that the simulation capability could promote industrial advancements through a quantitative design of innovative materials.