Polarizable Continuum Reaction-Field Solvation Models Affording Smooth Potential Energy Surfaces

Apparent surface charge, reaction-field solvation models often employ overlapping atomic spheres to represent the solute/continuum boundary. Discretization of the solute cavity surface, however, results in a boundary-element method that fails to afford a continuous potential energy surface for the solute. Several proposed remedies for this problem, based upon switching functions for the surface grid points and originally introduced for the conductor-like screening model (COSMO), are generalized here to an entire class of polarizable continuum models (PCMs). Gaussian blurring of the apparent surface charges proves to be crucial in order to avoid singularities in the reaction-field matrix and spurious oscillations in the energy gradient. The resulting “smooth PCMs” accelerate convergence of geometry optimizations and eliminate spurious peaks in vibrational spectra that are calculated by finite difference of analytic energy gradients.