Deep neural network based quantum simulations and quasichemical theory for accurate modeling of molten salt thermodynamics

With dual goals of efficient and accurate modeling of solvation thermodynamics in molten salt liquids, we employ ab initio molecular dynamics (AIMD) simulations, deep neural network interatomic potentials (NNIP), and quasichemical theory (QCT) to calculate the excess chemical potentials for the solute ions Na$^{+}$ and Cl$^{-}$ in the molten NaCl liquid. NNIP-based molecular dynamics simulations accelerate the calculations by 3 orders of magnitude and reduce the uncertainty to 1 kcal/mol. Using the Density Functional Theory (DFT) level of theory, the predicted excess chemical potential for the solute ion pair is -178.5$\pm$1.1 kcal/mol. A quantum correction of 13.7$\pm$1.9 kcal/mol is estimated via higher-level quantum chemistry calculations, leading to a final predicted ion pair excess chemical potential of -164.8$\pm$2.2 kcal/mol. The result is in good agreement with a value of $-163.5$ kcal/mol obtained from thermo-chemical tables. This study validates the application of QCT and NNIP simulations to the molten salt liquids, allowing for significant insights into the solvation thermodynamics crucial for numerous molten salt applications.