QM/EFP excitations: is polarizable embedding good enough?
Claudia I. Viquez Rojas & Lyudmila V. Slipchenko
Purdue University, Chemistry Department, West Lafayette, IN 47906
Hybrid quantum mechanics and molecular mechanics (QM/MM) methods are commonly used to explore the electronic structure of condensed phase systems. These hybrid methods enable the robust modeling of solute properties without neglecting the solute-solvent interactions. The effective fragment potential (EFP) is an accurate, yet computationally efficient method of representing the solvent. In the EFP model, the non-covalent interactions between effective fragments are described via electrostatics, polarization, dispersion and exchange repulsion contributions, while interactions between the QM and EFP subsystems have been typically limited to inclusion of electrostatic and polarization terms. In this study, we introduce several QM/EFP schemes that go beyond electrostatic and polarizable embedding. We examine the accuracy of these full-embedding schemes by analyzing the different electronic excitations of several model systems. We show that the description of excitation energies improves, with respect to the polarizable embedding scheme, when including exchange- repulsion interactions between the QM and classical regions; and deteriorates when smearing the electrostatic charges of the solvent.