Sanibel Symposium

The interface between the general Effective Fragment Potential (EFP2) method and the ab initio method (QM) has been implemented in GAMESS quantum chemistry package. QM/EFP2 captures the intermolecular interactions between the QM region and EFP fragments, which consists of Coulomb, polarization, exchange repulsion and dispersion components. This work presents the first benchmarking study of QM/EFP2 for the S22 and S66 databases. For both S22 and S66 datasets, the mean unsigned error (MUE) and standard deviation (SD) of the total interaction energies are less than 1 kcal/mol compared to CCSD(T)/CBS(haTZ) CP values. For the individual component energies, the MUE and SD are less than 3 kcal/mol and less than 1.5 kcal/mol for S22 and S66 datasets, respectively, in comparison with SAPT values. The errors can be attributed to the insufficient damping function for Coulomb term and/or the lack of damping for the polarization term, both of which affect the molecular orbital coefficients of the ab initio molecule and in turn, will affect exchange repulsion and dispersion energies. Moreover, the average difference between the two choices of QM region of all dimers is well under 1kcal/mol for the total interaction energies and component energies.