A COMPARATIVE-ANALYSIS BY MEANS OF QUANTUM MOLECULAR SIMILARITY MEASURES OF DENSITY DISTRIBUTIONS DERIVED FROM CONVENTIONAL AB-INITIO AND DENSITY-FUNCTIONAL METHODS

A procedure based on quantum molecular similarity measures (QMSM) has been used to compare electron densities obtained from conventional ab initio and density functional methodologies at their respective optimi zed geometries. This method has been applied to a series of small mole cules which have experimentally known properties and molecular bonds o f diverse degrees of ionicity and covalency. Results show that in most cases the electron densities obtained from density functional methodo logies are of a similar quality than post-Hartree-Fock generalized den sities. For molecules where Hartree-Fock methodology yields erroneous results, the density functional methodology is shown to yield usually more accurate densities than those provided by the second order Moller -Plesset perturbation theory. (C) 1996 American Institute of Physics.