Ion hydration is integral to biological functions, pharmaceutical applications, and future green-energy endeavors. Fluoride compounds, in particular, are known to react with water and play a major role in the stratospheric chemistry of chlorofluorocarbons. Classical molecular dynamics simulations have been able to predict numerous properties of fluoride hydration in agreement with experiment. However, classical simulations omit significant effects arising from the presence of light nuclei like hydrogen and the weakening of covalent OH bonds from the presence of FH bonding, or nuclear quantum effects. A complete understanding of fluoride hydration then necessitates treating these systems quantum mechanically. In this study, we employ path-integral-based quantum dynamical methods, along with MB-pol and MB-nrg, highly accurate data-driven many-body potentials for water and fluoride, respectively, to study the role of nuclear quantum effects in fluoride hydration. For our analysis of hydration structure as a function of solvation shells, we calculate radial and angular distribution functions. In our radial distribution functions, we observe a widening of peaks in each solvation shell due to the delocalization of H nuclei. In our angular distributions, we expect to find lower average HOH bond angles in water due to the electronegativity of fluoride. For hydration dynamics as a function of solvation shells, we calculate diffusion coefficients, mean residence times, and infrared spectra. Due to the strength of the FH bond, we expect lower diffusion coefficients and higher residence times with lower-numbered solvation shells. In our infrared spectra, we observe a second higher-frequency peak in the librations mode, higher frequencies in the bending mode, and lower frequencies in the asymmetric stretching mode of water, attributed to the presence of fluoride, delocalization of H nuclei, and the weakening of local OH bonds, respectively.
Understanding nuclear quantum effects in the solvation structure and hydrogen bond dynamics of fluoride hydration using many-body potentials
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