COMPARATIVE-STUDY OF THE MOLECULAR ELECTROSTATIC POTENTIAL OBTAINED FROM DIFFERENT WAVE-FUNCTIONS - RELIABILITY OF THE SEMIEMPIRICAL MNDO WAVE-FUNCTION

A systematic analysis of the molecular electrostatic potential (MEP) is presented. This study has been performed with a twofold purpose: first, to study the MEP dependence with regard to the quality of the basis set used to compute the ab initio SCF wavefunction and second, to develop and to assess a new strategy for computing isoelectrostatic potential maps using the semiempirical MNDO wavefunction. The only differences between this procedure and the ab initio SCF MEP computation lie in the freezing of the inner electrons and in the origin of the first‐order density matrix. The statistical analysis of MEPs computed for a large number of molecules from MNDO wavefunction and ab initio SCF wavefunctions obtained using STO‐3G, 4‐31G, 6‐31G, 4‐31G*, 6‐31G*, and 6‐31G** basis sets points out the ability of any wavefunction to reproduce the general topological characteristics of the MEP surfaces. Nevertheless, split‐valence basis sets including polarization functions are necessary to obtain accurate MEP minimum energy values. MNDO wavefunction tends to overestimate the MEP minima depth by a constant factor and shows an excellent ability to reflect the relative variation of MEP minima energies derived from a rather sophisticated (6‐31G*) basis set, lacking of the shortcomings detected in the semiempirical CNDO approximation. Copyright © 1990 John Wiley & Sons, Inc.