Probing the full cooperative structure of actinide chloride molten salts with Raman spectroscopy

Abstract Understanding the structure of molten actinide chlorides is essential for advancing modern molten salt reactors, but scattering experiments on these are extremely challenging and therefore almost nonexistent, while Raman spectra are not straightforward to interpret for systems with significant collective structure. As a result, allegedly predictive simulations of actinide melts are rarely validated against experimental structural information; hence these predictions can differ significantly. Here, we combine density functional theory-based ab initio molecular dynamics simulations accelerated to nanosecond timescales with machine learning force fields, Raman spectral modeling, and analysis of projected vibrational densities of states to assign spectral features and directly link them to liquid structure in molten ThCl 4 . We find that the melt forms a percolating Th–Cl network dominated by sevenfold coordination, with terminal Th–Cl vibrations generating the ~340 cm⁻¹ Raman band and edge- and face-sharing linkages producing the 250–300 cm⁻¹ shoulder. Quantitative agreement with experiment requires explicit semicore treatment (68 e effective core potential (ECP) with 5 d 10 retained) and dispersion corrections, whereas large-core ECPs systematically red-shift the spectrum. This validated protocol establishes Raman measurements coupled with first-principles simulations as a quantitative structural benchmark for more accurate modeling of chloride melts containing major and minor actinides when no scattering data are available.