Validity of the minimum polarizability principle in molecular vibrations and internal rotations: An ab initio SCF study

Molecular vibrations in ammonia (NH3) and hydrogen sulfide (H2S), and inter nal rotations in hydrogen peroxide (HOOH), hydrogen thioperoxide (HSOH), hy drogen persulfide (HSSH), and ethylene (C2H4) are studied using ab initio S CF methods at the Hartree-Fock level using:a-standard Pople 6-311G** basis set. Polarizability values are calculated using both Pople's and Sadlej's b asis sets, Any nontotally symmetric distortion in bond length or bond angle along the vibrational symmetry coordinates of a molecule around its equili brium geometry decreases the equilibrium hardness value and increases the:e quilibrium polarizability value, During rotational isomerization the minimu m energy conformation corresponds to the maximum hardness and minimum polar izability values and the maximum energy conformation corresponds to the min imum hardness and maximum polarizability values, Density functional calcula tions confirm these observed trends, In general we have found that the cond itions of maximum hardness and minimum polarizability complement the minimu m energy criterion for molecular stability.