AB-INITIO MOLECULAR-ORBITAL CALCULATIONS OF BOND INDEX AND VALENCY

This chapter reviews the applications of the quantitative definitions of bond index and valency for single determinant self-consistent-field (SCF) wavefunctions. A statistical interpretation of bond index is also presented. The chapter discusses the definitions of bond index and valency for correlated wavefunctions. Later, the results corresponding to SCF and correlated wavefunctions are discussed. The results of the calculations reviewed indicate that at the ground state equilibrium geometry of a molecule the SCF wavefunction is adequate for the study of its nature of bonding on the basis of bond indices and valencies. The latter quantities are sensitive to basis sets and the population analysis schemes. Generally basis sets of double-zeta quality augmented with a set of polarization and a set of diffuse functions (only in the case of highly ionic and/or negatively charged species) on highly electronegative centers should be employed in these calculations. Of the two schemes of population analysis—Mulliken's population analysis (MPA) and Löwdin population analysis (LPA) that are currently in use, the MPA generally gives a more consistent picture of bonding. © 1992 Academic Press Inc.