The hardness ( q ) , chemical potential ( p ) , and molecular valency (VM) profiles of CzH4, H3X-YH3 (X, Y = C, Si), B2H6, and H C P have been calculated ab initio using the 6-31G** basis set. These profiles correspond to rotation around the C=C bond in CzH4 and the X-Y bond in H3X-YH3, of the BHBH plane in B2H6, and of the H atom around the midpoint of the C P bond in HCP. The maximum hardness principle has been found to be obeyed in all cases. The q and p profiles are generally opposite in nature. With the exception of BzH6, the VM is maximum at the ground state equilibrium configuration of a molecule in all cases.

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Condensed Fukui function values of a number of closed-shell molecules have been calculated from Stockholder charges which were obtained using ab initio HF and DFT/B3LYP methods. The global softness parameters needed to evaluate local softness have been calculated using both Koopmans' approximation and the energy difference method. The calculated reactivity indices (condensed Fukui function and atomic softness) were used to predict the sites of electrophilic and nucleophilic attack in the molecules under investigation. In all cases, the atoms with the maximal value of condensed Fukui function and local softness are predicted to be the preferred sites of electrophilic or nucleophilic addition. The predictions thus made are in agreement with experiment and independent of the theoretical models used. The performance of the relative electrophilicity and relative nucleophilicity indices also was tested, but they were found not to have any special advantage as local reactivity descriptors.

Atomic charges, bond indices (two-center and three-center), and valences have been calculated for a number of closed-shell molecules using ab initio Hartree−Fock (HF) and Kohn−Sham (KS) orbitals. In a few molecules we have also studied the variation of molecular valence, orbital energy and orbital valence with bond angle. Several basis sets and population analysis schemes have been employed in the present calculations. It is observed that, compared to the HF orbitals, the KS orbitals predict a slightly enhanced covalency. Otherwise, at least on the basis of bond index and related concepts, no appreciable difference is noticed between their performance in the theoretical study of bonding.