Soft-Sphere Continuum Solvation in Electronic-Structure Calculations

Abstract

We present an implicit solvation approach where the interface between the quantum-mechanical solute and the surrounding environment is described by a fully continuous permittivity built up with atomic-centered "soft" spheres. This approach combines many of the advantages of the self-consistent continuum solvation model in handling solutes and surfaces in contact with complex dielectric environments or electrolytes in electronic-structure calculations. In addition it is able to describe accurately both neutral and charged systems. The continuous function, describing the variation of the permittivity, allows to compute analytically the nonelectrostatic contributions to the solvation free energy that are described in terms of the quantum surface. The whole methodology is computationally stable, provides consistent energies and forces, and keeps the computational efforts and runtimes comparable to those of standard vacuum calculations. The capabilitiy to treat arbitrary molecular or slab-like geometries as well as charged molecules is key to tackle electrolytes within mixed explicit/implicit frameworks. We show that, with given, fixed atomic radii, two parameters are sufficient to give a mean absolute error of only 1.12 kcal/mol with respect to the experimental aqueous solvation energies for a set of 274 neutral solutes. For charged systems, the same set of parameters provides solvation energies for a set of 60 anions and 52 cations with an error of 2.96 and 2.13 kcal/mol, respectively, improving upon previous literature values. To tackle elements not present in most solvation databases, a new benchmark scheme on wettability and contact angles is proposed for solid-liquid interfaces and applied to the investigation of the stable terminations of a CdS (112̅0) surface in an electrochemical medium.

Surface reconstruction of fluorites in vacuum and aqueous environment

“…Different coverages were modeled by adding an increasing number of water molecules. In the second approach, the aqueous environment was modeled at the DFT level by means of a recently developed implicit solvation model [45,46] which replaces the explicit water molecules by a continuum body surrounding the quantum-mechanical system. This implicit approach allowed efficient minima hopping explorations of the potential energy surface for hydrated fluorite terminations.…”

“…We employed the soft-sphere continuum solvation model [45,46] to explore the solvent-surface interaction by including the solvent as a continuum at the DFT level. Within this approach, the interface between the quantum-mechanical solute and surrounding environment is described by a fully continuum and differentiable permittivity (r) function of the atomic coordinates.…”

“…Nonelectrostatic contributions to the solvation free energy (which represent the nonelectrostatic interactions between the solute and the solvent) linearly depend on the cavity quantum surface by means of a proportional prefactor α + γ (γ is the solvent surface tension and α a tunable parameter). Both α and f are fitted to an experimental dataset of solvation free energies of small molecules or to wetting properties of solid-liquid interfaces [46].…”

“…This explicit inclusion of water should be in principle the most accurate to account for solvent effects, albeit fully explicit ab-initio approaches result in well-known limitations in describing an aqueous environment, in particular regarding its structural and dielectric properties [42][43][44]. In order to reduce the large number of degrees of freedom of the explicit solvent model, which gives many different configurations of the water molecules for identical surface reconstructions, we employ in addition a recently developed implicit solvation model [45,46]. Using this method, we explore the potential energy surface of the hydrated surface reconstructions.…”

Molecular Dynamics Investigation of the Dielectric Decrement of Ion Solutions

“…Despite its importance for various chemical and biological processes, such as fuel cells or ion channels,, and the extensive research into this direction over the years, the exact nature of the electric double layer (EDL) is still not fully understood at the molecular level. Attempts to accurately model the electrode electrolyte interface are often carried out with the help of continuum models to avoid the computational costs of explicitly including a large amount of electrolyte molecules. The Poisson‐Boltzmann theory is a simple yet powerful tool to model aqueous ion solutions.…”