A smooth solvation potential based on the conductor-like screening model

The development of a smooth solvation potential from which analytic derivat ives can be derived is important for molecular applications that require ge ometry optimization and conformational sampling. Derivatives in conventiona l boundary element solvation methods are typically treated approximately, a nd contain singularities that arise from discontinuities in the potential. We present a simple smooth solvation potential that is based on the conduct or-like screening model proposed by Klamt and Schuurmann (Klamt, A.; Schuur mann, G. J. Chem. Sec., Perkin. Trans. 2, 1993, 799). The model uses a simp le solvent accessible surface with an atomic sphere discretization based on high-order angular quadrature schemes for spherical harmonics. Surface ele ments are modeled by spherical Gaussian functions with exponents calibrated to obtain the exact Born ion energy and uniform surface charge density and to avoid Coulomb singularities present in conventional point-charge surfac e element models. The set of linear equations are modified to produce a rig orously smooth solvation potential by allowing the effect of new surface el ements to be turned on or off over a finite switching region around each at om. Numerical tests of the method are provided, in addition to discussions of rotational variance, generalization to arbitrary internal dielectric, us e of constraints, and extension to a smooth surface area model.