An integrated effective fragment-polarizable continuum approach to solvation: Theory and application to glycine

A new discrete/continuum solvation model has been developed by combining the effective fragment potential EFP for the discrete part and the polarizable continuum model PCM for the continuum part. The usefulness of this model is demonstrated by applying it to the calculation of the relative energies of the neutral and zwitterionic forms of glycine. These calculations were performed by treating glycine with ab initio wave functions. Water clusters were treated with both ab initio and EFP methods for comparison purposes, and the effect of the continuum was accounted for by the PCM model. The energy barrier connecting the zwitterionic and neutral three-water clusters was also examined. The computationally efficient EFP/PCM model gives results that are in close agreement with the much more expensive full ab initio/PCM calculation. The use of methods that account for electron correlation is necessary to obtain accurate relative energies for the isomers of glycine.