COVALENT BOND ORDERS AND ATOMIC VALENCE INDEXES IN THE TOPOLOGICAL THEORY OF ATOMS IN MOLECULES

Quantum chemical counterparts are defined for chemical concepts of bon d order (multiplicity) and actual valence of an atom in a molecule by performing an atomic partitioning of the exchange part of the second-o rder density matrix within the framework of Bader's topological theory of atoms in molecules. Unlike previous definitions, the present resul ts permit the formulation of the concepts of bond order and valence in a basis set independent manner and extend, therefore, their applicabi lity to the Hartree-Fock limit or even exact wave functions. The numer ical results obtained indicate that, in the framework of Bader's theor y, bond ionicities are much greater than usually supposed on the basis of conventional population analyses, and this is reflected by a signi ficant reduction of covalent bond order and valence values.