Screened Electrostatically Embedded Many-Body Method

The electrostatically embedded many-body (EE-MB) method has been very successful for calculating energies of molecular clusters. Here, we introduce screened charges in the EE-MB method and evaluate the accuracy of the resulting method for calculating the binding energy for five water hexamers. The screened EE-MB method shows dramatic improvement over the unscreened method. The mean unsigned deviation of the screened EE-MB binding energies relative to unfragmented calculations on the entire cluster is 0.60 kcal/mol at the pairwise additive (PA) level of approximation and 0.24 kcal/mol at the three-body (3B) level, as compared to mean unsigned deviations of 1.32 (PA) and 0.54 (3B) kcal/mol with unscreened charges. The mean unsigned percentage deviations with screened embedding are only 1.1% (PA) and 0.5% (3B). The high accuracy obtained with the very affordable and quadratically scaling PA method is very encouraging and opens the door to more accurate simulations on complex systems.