HPAM: Hirshfeld partitioned atomic multipoles Original Research Article

An implementation of the Hirshfeld (HD) and Hirshfeld-Iterated (HD-I) atomic charge density partitioning schemes is described. Atomic charges and atomic multipoles are calculated from the HD and HD-I atomic charge densities for arbitrary atomic multipole rank image on molecules of arbitrary shape and size. The HD and HD-I atomic charges/multipoles are tested by comparing molecular multipole moments and the electrostatic potential (ESP) surrounding a molecule with their reference ab initio values. In general, the HD-I atomic charges/multipoles are found to better reproduce ab initio electrostatic properties over HD atomic charges/multipoles. A systematic increase in precision for reproducing ab initio electrostatic properties is demonstrated by increasing the atomic multipole rank from image (atomic charges) to image (atomic hexadecapoles). Both HD and HD-I atomic multipoles up to rank image are shown to exactly reproduce ab initio molecular multipole moments of rank L for image. In addition, molecular dipole moments calculated by HD, HD-I, and ChelpG atomic charges only (image) are compared with reference ab initio values. Significant errors in reproducing ab initio molecular dipole moments are found if only HD or HD-I atomic charges used.