Multipole electrostatic model for MNDO-like techniques with minimal valence spd-basis sets

We report an implementation of an atomic multipole model (up to quadrupole) for calculating the electrostatic properties of molecules based on electron densities derived from MNDO-like NDDO-based semiempirical MO calculations with minimal s,p,d valence basis sets. The results were validated by a comparison of the calculated values of the molecular electrostatic potential with those obtained from fine grain numerical integrations (both with AM1*), B3LYP/6–31G(d) and MP2/6–31G(d). The DFT and ab initio potentials can be reproduced remarkably well (mean unsigned error <2 kcal mol⁻¹ e⁻¹) using simple linear regression equations to correct the AM1* (multipole) results. Dedicated to Prof. Karl Jug on the occasion of his 65th birthday