An interacting segment model of molecular electric tensor properties: Application to dipole moments, polarizabilities, and hyperpolarizabilities for the halogenated methanes

A previously developed interacting segment model [ISM-see J. Chem. Phys. 67, 2109 (1977)] is applied to a full-scale treatment of the electric dipole moments, isotropic and anisotropic polarizabilities, and hyperpolarizabilities of a series of 12 halogenated methane molecules CX_n Y _4-n(X,Y=H,F,C1; n=0-4). The ISM scheme enables the molecular properties considered to be fitted in terms of a set of "bare" electric tensor parameters for each bond, which are modified ("dressed") by intramolecular electrostatic interactions. The computed results of the ISM scheme, and of a corresponding interaction-free bond additivity model, are discussed in relation to the following: choice of geometric and bond parameters, quality of fit to experimentally determined molecular and bond properties, and predictive potential and general physical validity of the model. It is concluded that the ISM approach represents a substantial improvement over simple bond additivity as a basis for understanding molecular electric tensor properties.