Static polarizabilities and hyperpolarizabilities, and multipole moments for Cl 2 and Br 2. Electron correlation and molecular vibration effects

Abstract

Ab initio calculations of the quadrupole and hexadecapole moments, and the static dipole polarizabilities and hyperpolarizabilities are reported for Cl 2 and Br 2. These calculations allow for both electron correlation and molecular vibration. The electronic contributions to the various properties are calculated by finite-field, fourth-order, many-body perturbation theory at three bond lengths, and then averaged over the zero point vibrations. The pure vibrational hyperpolarizabilities are calculated using sum-over-vibrational-states expressions; the requisite matrix elements are calculated with numerical vibrational wavefunctions and the electronic dipole polarizabilities as a function of bond length. The vibrational hyperpolarizabilities are found to be sizable fractions of the electronic hyperpolarizabilities, especially for the longitudinal component. Electron correlation effects are shown to be important for both the electronic and the vibrational hyperpolarizabilities. The calculations are in good agreement with available experimental values.