We propose a novel approach toward calculating activation and reaction volumes based on MD simulations of reaction systems. The accuracy of the calculated volumes, verified by the comparison to the experimental data, is suitable for quantitative analysis of the experimental volumes of activations in terms of structural parameters of the corresponding transition states.

Experimentally, the effects of pressure on reaction rates are described by their pressure derivatives, known as volumes of activation. Transition state theory directly links activation volumes to partial molar volumes of reactants and transition states. We discuss a molecular dynamics method for the accurate calculation of molecular volumes, within which the volumes of molecular species are obtained as a difference between the volumes of pure solvent and solvent with a single molecule inserted. The volumes thus obtained depend on the molecular geometry, the strength and type of the solute-solvent interactions, as well as temperature and pressure. The partial molar volumes calculated using this approach agree well with experimental data. Since this method can also be applied to transition state species, it allows for quantitative analysis of experimental volumes of activation in terms of structural parameters of the corresponding transition states. The efficiency of the approach is illustrated by calculation of volumes of activation for three nonpolar reactions in nonpolar solvents. The results agree well with the experimental data.

We present a modified form of the Functionalized Cahn Hilliard (FCH) functional which models highly amphiphilic systems in solvent. A molecule is highly amphiphilic if the energy of a molecule isolated within the bulk solvent molecule is prohibitively high. For such systems once the amphiphilic molecules assemble into a structure it is very rare for a molecule to exchange back into the bulk. The highly amphiphilic FCH functional has a well with limited smoothness and admits compactly supported critical points. In the limit of molecular length ε → 0 we consider sequences with bounded energy whose support resides within an ε-neighborhood of a fixed codimension one interface. We show that the FCH energy is uniformly bounded below, independent of ε > 0, and identify assumptions on tangential variation of sequences that guarantee the existence of subsequences that converge to a weak solution of a rescaled bilayer profile equation, and show that sequences with limited tangential variation enjoy a lim inf inequality. For fixed codimension one interfaces we construct bounded energy sequences which converge to the bilayer profile and others with larger tangential variation which do not converge to the bilayer profile but whose limiting energy can violate the lim inf inequality, depending upon the energy parameters.