Calculation of Molecular Volumes and Volumes of Activation Using Molecular Dynamics Simulations

Traditionally, the effects of pressure on the reaction rates are expressed in terms of their pressure derivatives, known as volumes of activation. Within the framework of transition-state theory, these volumes of activation can be identified with the difference in volumes of transition states and reactants. Because the volumes of reactants are readily available experimentally, the volumes of activation provide a direct measure of the transition-state volumes and thus a unique glimpse of these transient species. We propose a new approach toward calculating molecular volumes based on molecular dynamics simulations. Molecular volumes and volumes of activation for nonpolar systems calculated using this approach agree well with the experimental data.