Soft-Sphere Continuum Solvation in Electronic-Structure\nCalculations

Abstract

We\npresent an implicit solvation approach where the interface between\nthe quantum-mechanical solute and the surrounding environment is described\nby a fully continuous permittivity built up with atomic-centered “soft”\nspheres. This approach combines many of the advantages of the self-consistent\ncontinuum solvation model in handling solutes and surfaces in contact\nwith complex dielectric environments or electrolytes in electronic-structure\ncalculations. In addition it is able to describe accurately both neutral\nand charged systems. The continuous function, describing the variation\nof the permittivity, allows to compute analytically the nonelectrostatic\ncontributions to the solvation free energy that are described in terms\nof the quantum surface. The whole methodology is computationally stable,\nprovides consistent energies and forces, and keeps the computational\nefforts and runtimes comparable to those of standard vacuum calculations.\nThe capabilitiy to treat arbitrary molecular or slab-like geometries\nas well as charged molecules is key to tackle electrolytes within\nmixed explicit/implicit frameworks. We show that, with given, fixed\natomic radii, two parameters are sufficient to give a mean absolute\nerror of only 1.12 kcal/mol with respect to the experimental aqueous\nsolvation energies for a set of 274 neutral solutes. For charged systems,\nthe same set of parameters provides solvation energies for a set of\n60 anions and 52 cations with an error of 2.96 and 2.13 kcal/mol,\nrespectively, improving upon previous literature values. To tackle\nelements not present in most solvation databases, a new benchmark\nscheme on wettability and contact angles is proposed for solid–liquid\ninterfaces and applied to the investigation of the stable terminations\nof a CdS (112̅0) surface in an electrochemical medium.