Potential derived charges using a geodesic point selection scheme

Potential derived (PD) atomic charges, obtained by fitting to molecular electrostatic potentials, are widely used in molecular modeling and simulation calculations. These charges are known to depend on the sample of points chosen for the fit, on the particular point selection algorithm, on molecular translations and rotations in many instances, and even on molecular conformation. Following a critique of currently available methods, a novel point selection scheme is described which results in a highly isotropic array of points located on a series of fused-sphere van der Waals surfaces. The pattern of points is based on tesselations of the icosahedron, and these are discussed in some detail along with their connection with virus morphology, geodesic domes, and symmetric fullerene structures. Using methanol as a test case, it is shown that the new method leads to PD charges which are independent of translation and display minimal rotational dependence, and are hence far better suited to the determination of PD charges from electrostatic potentials obtained from both theory and experimental X-ray diffraction data. The conformation dependence of the newly derived PD charges for alanyl dipeptide is found to be substantially less than obtained earlier by Williams [Biopolymers 29, 1367 (1990)]. (C) 1996 by John Wiley & Sons, Inc.