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Potential energy barrier for proton transfer in compressed benzoic acid

Benzoic acid (BA) is a model system for studying proton transfer (PT) reactions. The properties of solid BA subject to high pressure (exceeding 1 kbar = 0.1 GPa) are of particular interest due to the possibility of compression-tuning of the PT barrier. Here we present a simulations aimed a evaluating the value of this barrier in solid BA in the 1 atm - 15 GPa pressure range. We find that pressure-induced shortening of the O...O contacts within the BA dimers leads to a decrease in PT barrier, and subsequent symmetrization of the hydrogen bond. However, this effect is obtained only after taking into account zero-point energy (ZPE) differences between BA tautomers and the transition state. The obtained results shed light on previous experiments on compressed benzoic acid, and indicate that a common scaling behavior with respect to O...O distance might be applicable for hydrogen-bond symmetrization in both organic and inorganic systems.