PNNL

Abstract

This paper presents recent developments in the COSMO solvation model implementation in NWChem. A new cavity construction approach based on the solvent-excluding surface (SES), using the well-established GEPOL algorithm, has been introduced. Additionally, a straightforward procedure to merge surface segments that are too close—often a source of numerical artifacts—has been implemented. The available methods for correcting outlying surface charges have also been reviewed and improved. To validate the new implementation, we computed dielectric solvation energies for a chemically diverse set of approximately 100 molecules, including neutral species, small ions, and common ionic liquid components. Results were compared against those from GAMESS using the double-cavity method as a reference. Although the double-cavity approach can be regarded as more accurate, the simpler correction schemes available in NWChem—based on scaling factors or Lagrange multipliers— can achieve excellent agreement if the potential is also properly corrected, with mean unsigned deviations around 0.15 kcal/mol. Prediction of typical vapor-liquid and liquid-liquid equilibria using a COSMO-SAC variant based on NWChem also showed very promising results.