QM/MM Simulations with the Gaussian Electrostatic Model: A Density-based Polarizable Potential

Abstract

The use of advanced polarizable potentials in quantum mechanical/molecular mechanical (QM/MM) simulations has been shown to improve the overall accuracy of the calculation. We have developed a density-based potential called the Gaussian electrostatic model (GEM), which has been shown to provide very accurate environments for QM wave functions in QM/MM. In this contribution we present a new implementation of QM/GEM that extends our implementation to include all components (Coulomb, exchange-repulsion, polarization, and dispersion) for the total intermolecular interaction energy in QM/MM calculations, except for the charge-transfer term. The accuracy of the method is tested using a subset of water dimers from the water dimer potential energy surface reported by Babin et al. ( J. Chem. Theory Comput. 2013 9, 5395-5403). Additionally, results of the new implementation are contrasted with results obtained with the classical AMOEBA potential. Our results indicate that GEM provides an accurate MM environment with average root-mean-square error <0.15 kcal/mol for every intermolecular interaction energy component compared with SAPT2+3/aug-cc-pVTZ reference calculations.

Figure 1.

Errors per cluster with respect to SAPT. The errors corresponding to the Coulomb interaction energy are depicted on the first column, and the errors corresponding to the exchange interaction energy are given on the second column. The computed errors for the sum of dispersion and polarization energies are depicted on the third, while the error for total energy is given on the fourth column.

Figure 2.

Total intermolecular interaction energy errors per cluster for QM/AMOEBA with respect to SAPT.