Hybrid Cluster-Continuum Method for Single-Ion Solvation Free Energy in Acetonitrile Solvent

A new hybrid discrete-continuum approach named the cluster-continuum
static approximation (CCSA) has been proposed for acetonitrile solvent.
The continuum part uses the conductor-like polarizable continuum model
for electrostatic and a surface area-dependent term for nonelectrostatic
solvation. The CCSA includes only one explicit acetonitrile solvent
molecule and a damping function, which makes the CCSA method reduce
to pure continuum solvation in the case of weaker potential of mean
force for solute–solvent interaction. The performance of the
model was tested for 22 anions and 22 cations, including challenge
species that cannot be adequately described by pure continuum solvation.
A comparison was done with the widely used solvent model density (SMD)
model. For anions, the CCSA reduces to pure continuum solvation and
the method has the same performance as the SMD model, with a standard
deviation of the mean signed error (SD-MSE) of 2.7 kcal mol–1 for both models. However, the CCSA method for cations considerably
outperforms the SMD model, with an SD-MSE of 3.3 kcal mol–1 for the former and 8.4 kcal mol–1 for the latter.
The method can be automated, and the present study suggests that continuum
solvation models could be parameterized taking into account the explicit
solvation as proposed in this work.