Raman spectroscopy has been extensively used for more than 50 years to probe the local structure of molten salts. However, the interpretation of the experimental spectra in many cases is problematic, resulting in several debates that persist to date. To avoid such ambiguities, it is highly desirable to develop an approach to compute the Raman spectra of molten salts. A normal mode analysis routinely used for solids cannot be readily applied to molten salts, requiring a computation of a time-depended polarizability tensor. In our recent work, we have developed a capability to simulate Raman spectra of molten salts from ab initio molecular dynamics simulations. This is accomplished by Fourier transformation of time autocorrelation functions involving the appropriate polarizability tensor components of the full periodic simulation cell computed directly from the wave function using the correct quantum chemical operator from modern theory of polarization. In this work, we will present several examples of the simulated Raman spectra of molten salts containing MgCl2, LaCl3, and ZrF4 that show a remarkable agreement with the experimental spectra. This allows us to interpret the old experimental Raman spectra in a new way and firmly establish several trends in the local structure of molten salts across a wide range of compositions.

Simulation and reinterpretation of the Raman spectra of molten salts using ab inito molecular dynamics

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