Electrostatic properties of small molecules by means of atomic multipoles from the quantum theory of atoms in molecules

Abstract

AbstractAtomic multipoles from the Quantum Theory of Atoms in Molecules (QTAIM), up to quadrupoles, and CHELPG charges are employed in the description of electrostatic properties of some small linear molecules: H2, HF, HCl, HBr, HCN, HNC, and CO. A proton is placed on the molecular axis in distances within the range 3–8 Å from the terminal atoms. The polarization of molecular electronic densities induced by the proton is readily included by the calculation of atomic multipoles in each proton‐molecule arrangement. Electrostatic potentials at the proton position as given by QTAIM multipoles are always in better agreement with the reference results, calculated directly at the B3LYP/6‐311G(3d,3p) level, than those predicted with CHELPG charges, particularly for cases in which QTAIM multipoles showed that the contribution of atomic charges to these potentials is not clearly predominant over other contributions as in H2, HCl, HBr, HNC, and CO. The lone pair at the carbon atoms in CO and HNC, as described by QTAIM atomic dipoles, is indispensable in studies of electrostatic properties of these molecules. Moreover, QTAIM multipoles are also able to describe properly the large polarizations induced by the proton along the proton‐molecule distances studied. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008