A NONEMPIRICAL ELECTRONEGATIVITY EQUALIZATION SCHEME - THEORY AND APPLICATIONS USING ISOLATED ATOM PROPERTIES

The electronegativity equalization principle, originally formulated by Sanderson and proven quantum mechanically by Parr et al., within the framework of density functional theory, is studied numerically. A firs t order expression for the electronegativity chi of an atom A in a mol ecule is derived, based on the change, upon molecule formation, of the number of electrons N-A and the external potential nu(A)(r) of this a tom with respect to the isolated atom case. The relative importance of the two corrections to the isolated atom electronegativity is discuss ed. Furthermore, the expression was identified with other density func tional theory based electronegativity equalization formalisms and was applied to small molecular systems: the resulting charge distributions and molecular electronegativities showed a fair correlation with othe r estimations for these quantities. The importance of second order ter ms is also discussed, together with an extension, permitting the use o f functional group electronegativities and hardnesses.