Effect of Molecular Orientational Correlations on Solvation Free Energy Computed by Reference Interaction Site Model Theory

The effect of molecular
orientational correlations on the solvation
free energy (SFE) of one-dimensional and three-dimensional reference
interaction site models (1D- and 3D-RISM) is investigated. The repulsive
bridge correction (RBC) and the partial wave (PW) expansion are representative
approaches for accounting for the orientational correlation partially
lacking in original 1D- and 3D-RISM. The SFEs of 1D- and 3D-RISM for
a set of small organic molecules are compared with the simulation
results. Accordingly, the SFE expressions, based on RBC and PW, provide
more accurate results than those of the uncorrected HNC or KH SFE expressions, which indicates that accounting for molecular
orientational dependencies significantly contributes to the improvement
of the SFE. The SFE component analysis indicates that the nonpolar
component mainly contributes to the correction. The dependence of
the error in the RISM SFE on the number of solute sites is examined.
In addition, we discuss the differences between 1D- and 3D-RISM through
the effect of these corrections.