On the use of mixed basis sets to compute accurate molecular electrostatic potentials

Abstract

A procedure for computing molecular electrostatic potentials (MEPs) at low computational cost is tested. Analysis of MEPs derived from SCF wavefunctions computed using STO-3G, 6-31G and 6-31 G* basis sets reveals the marked influence of the basis set on the well depth and the location of minima. Both minimal and split-valence basis sets overestimate the MEP well depth and underestimate the distance from minima to nuclei; inclusion of polarization functions is necessary to provide reliable values for these quantities. We use a mixed basis set, which assigns split-valenceand minimal basis sets to heavy and hydrogen atoms, respectively. Polarization functions are also included, but limited to atoms bearing lone pairs. A 6-31 G*/3-21G/STO-3G mixed basis set is proposed as a reliable method for studying chemical and biochemical systems.