Development of a Model That Contains Both Multipole Moments and Gaussians for the Calculation of Molecular Electrostatic Potentials

摘要

The electrostatic interaction is a critical component of intermolecular interactions in biological processes. Rapid methods for the computation and characterization of the molecular electrostatic potential (MEP) that segment the molecular charge distribution and replace this continuous function by a series of multipole moments for each segment have been described. There are two sources of error in these techniques: (1) The truncation of the expansion after just a few terms, (2) The charge in the segmental distribution that is more distant from the expansion center than the observation point. In order to expand this range a method is introduced that uses exact techniques to compute the MEP for the part of the molecular charge distribution described by the gaussians on each atom with the smallest exponential parameter and uses segmental multipole methods for the remainder of the charge. Using pyrrole with an STO-3g wave function as an example, this method significantly improves the potential in the range 1.4-2.0 A from atoms with only an increase of 1% in computational effort needed when compared to a computation of the exact potential. If other basis sets are used with more diffuse gaussians the convergence of the multipole expansion will be at greater distances from the atoms and this type of correction will be more important.