The recent Hartree-Fock (HF) difference approach to the chemical valen
ce indices (ionic and covalent), formulated in the framework of the pa
ir-density matrix, is implemented within the Kohn-Sham (KS) density fu
nctional theory (DFT). The valence numbers are quadratic in terms of d
isplacements of the molecular spin-resolved charge-and-bond-order (CBO
) matrix elements, relative to values in the separated atoms limit (SA
L). It is shown that the global valence represents a generalized ''dis
tance'' quantity measuring a degree of similarity between the two CBO
matrices: the molecular and SAL. Numerical values for typical molecule
s exhibiting single and multiple bonds demonstrate that the KS orbital
s give rise to these new bond valences in good agreement with both che
mical and HF predictions. This KS bond multiplicity analysis is applie
d to the chemisorption system including the allyl radical and a model
surface cluster of molybdenum oxide. It is concluded that the quadrati
c valence analysis represents a valuable procedure for extracting usef
ul chemical information from standard DFT calculations. (C) 1997 John
Wiley & Sons, Inc.