Ab initio calculation of electrostatic multipoles with Wannier functions for large-scale biomolecular simulations.

It has long been known that accurate electrostatics is a key issue for improving current force fields for large-scale biomolecular simulations. Typically, this calls for an improved and more accurate description of the molecular electrostatic potential, which eliminates the artifacts associated with current point charge-based descriptions. In turn, this involves the partitioning of the extended molecular charge distribution, so that charges and multipole moments can be assigned to different atoms. As an alternate to current approaches, we have investigated a charge partitioning scheme that is based on the maximally localized Wannier functions. This has the advantage of partitioning the charge, and placing it around the molecule in a chemically meaningful manner. Moreover, higher order multipoles may all be calculated without any undue numerical difficulties. Tests on isolated molecules and water dimers, show that the molecular electrostatic potentials generated by such a Wannier-function based approach are in excellent agreement with the density functional-based calculations.