Generalizing Continuum Solvation in Crystal to Nonaqueous Solvents: Implementation, Parametrization, and Application to Molecules and Surfaces

Can We Unambiguously Define the Dipole Moment of Molecules in the Condensed Phase?

Various theoretical methods were applied and evaluated to determine the dipole moment of polar protic (methanol, ethanol) and aprotic (acetonitrile, pyridine, acetone) dipoles in the crystal phase. In mono-alcohols, the dipole moment is influenced by the hydrogen bonding (H-bonding) environment, similarly to earlier findings with liquid water. Using localization techniques without considering the effect of neighboring molecules gives similar results for the dipole moment of mono-alcohols than those obtained from the polarized continuum model (PCM). However, the PCM for polar aprotic molecules provides significantly different dipole moment values compared to localization methods. Our results clearly show that the magnitude of the dipole moment in the condensed phase cannot be unambiguously determined.

Solv: An Alternative Continuum Model Implementation Based on Fixed Atomic Charges, Scaled Particle Theory, and the Atom-Atom Potential Method

An alternative continuum model implementation is reported. The electrostatic contribution to the solvation Gibbs free energy utilizes the noniterative conductor-like screening model of Vyboishchikov and Voityuk (DOI: 10.1002/jcc.26531) based on the fixed partial atomic charges. The nonelectrostatic solute-solvent dispersion-repulsion energy is calculated through the Caillet-Claverie atom-atom potential method employing the grid-based approach. The nonelectrostatic cavitation energy is computed within the scaled particle theory (SPT) formalism with the solute hard-sphere radius obtained via the Pierotti-Claverie (PC) scheme, from the solute molecular surface (SPT-S) or volume (SPT-V). The solvent hard-sphere radius is derived through the fitting to the experimental total solvation free energies of 2530 neutral species in 92 solvents. Application of the model to reproduce both the absolute and relative (reaction net) solvation free energies indicates that the SPT-V approach based on the CM5 charges is the best performer. The method is suggested for the solvation free energy calculation in the nonaqueous solvents.

Towards a transferable nonelectrostatic model for continuum solvation: The electrostatic and nonelectrostatic energy correction model

In this work, we introduce an electrostatic and non-electrostatic (ENE) correction to the solvation energy based on the Solvent-Accessible Surface Area (SASA) of the solute and the solvent static dielectric constant. The proposed correction was developed for neutral solutes in non-aqueous solvents, considering three different implicit solvation models based on a Self-Consistent Reaction Field treatment of solute-solvent mutual polarization using an Apparent Surface Charge formalism, namely the Integral Equation Formalism of the Polarizable Continuum Model using a continuous surface charge scheme (PCM), the Solvation Model based on solute electron density (SMD), and the generalized Finite-Difference Poisson-Boltzmann (FDPB) model. The proposed correction was parametrized on a diverse training set of 4980 solvation data from the Solv@tum database of experimental solvation energies, and validated on the non-aqueous subset of the MNSOL database comprising 2140 solvation energies. The performances of the proposed ENE models with minimal and extended parameters formulations have been analyzed and the latter variant has been further compared to the widely used Cavity, Dispersion, and Solvent structural effects (CDS) non-electrostatic model originally developed for the SMx family of implicit solvation models. Overall, a very good agreement between the computed solvation energies with the ENE correction and the reference experimental data has been found on both the training and test sets for all continuum solvation models considered. Furthermore, results for the ENE correction are on par with the reference CDS non-electrostatic model for both SMD and FDPB electrostatics, but with the advantage of using a lower number of parameters and thus an improved transferability between different electrostatics treatments.