  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.
