Ultrafast QM/MM calculations with electronic charge embedding

by Pulay, Peter; Dupuis, Michel

A highly efficient method is introduced for QM/MM calcns. with electronic embedding. It obviates the need to perform a high-level electronic structure calcn. for every solvent or environment configuration. The response of the system to the long-range electrostatic field of the environment is evaluated using precalcd. generalized elec. moments and polarizabilities. The latter are the first and second order responses of the system to spatially modulated elec. fields. The elec. potential of the surrounding is evaluated on a grid within the mol. and fitted to inverse powers at distributed centers. Calcn. of the total response from precalcd. responses is orders of magnitude faster than a new electronic structure calcn. The main projected use of this method is to perform thermodn. simulations, for instance Monte Carlo simulations in solns. Reliable statistics, which requires averaging over millions of configurations, can be collected efficiently using data from a limited no. of high-level calcns.