Modeling Metallic Halide Local Structures in Salt Melts Using a Genetic Algorithm

Abstract

Knowing the local structure of metal ions in molten salt melts is essential for understanding the chemistry related to corrosion and solvation processes for various applications such as molten salt reactors, solar thermal power systems, and molten salt-enabled materials processing. However, modeling the dynamic local structure of metals in salt melts is difficult because classical mechanics does not reproduce the correct local atomic networking. The computational cost of carrying out multiple first-principles dynamics calculations to ensure that the compositional space is well sampled can be prohibitively large. In order to address this issue, the current study explores the use of the evolutionary algorithm Universal Structure Predictor: Evolutionary Xtallography (USPEX) to predict coordination numbers of strontium and zirconium in binary and ternary chloride and fluoride melts. Temperature-dependent coordination number distributions for the metal atoms were computed using a Boltzmann distribution. The calculated average coordination numbers were found to be consistent with observations from extended X-ray absorption fine structure (EXAFS) experiments and the expected temperature trends. Furthermore, the most stable predicted crystal structures compare well with EXAFS values, validating our approach for predicting local structures in salt melts.

Effect of XC functionals and dispersion corrections on the DFT‐computed structural and vibrational properties of SrCl2–NaCl and ZrF4–LiF

“…Insights generated for solids are also useful for interpreting the Raman spectra of the melt. [32] Dracopoulos and Papatheodorou have demonstrated in multiple studies that the most intense bands in the Raman spectra of the solid phase often remain intense in the molten state, albeit with shifts in wavenumbers and broadening. [17,33,34] Thus, our findings from this study can be valuable for interpreting Raman spectra of the melt.…”

“…Our study primarily focuses on predicting the phonon properties of these salts. Insights generated for solids are also useful for interpreting the Raman spectra of the melt [32] . Dracopoulos and Papatheodorou have demonstrated in multiple studies that the most intense bands in the Raman spectra of the solid phase often remain intense in the molten state, albeit with shifts in wavenumbers and broadening [17,33,34] .…”