Linear response coupled cluster calculation of Raman scattering cross sections.

The linear response coupled cluster singles and doubles (CCSD) method has been used to evaluate electric dipole polarizabilities, their geometric derivatives and Q-branch Raman scattering cross sections for five diatomic molecules: N$_2$, CO, HF, HCl and Cl$_2$. A systematic study of basis set convergence has been carried out. Geometric derivatives of the frequency dispersion coefficients have been computed. This allowed to evaluate Raman intensities for arbitrary laser frequencies outside the resonance region. The geometric derivatives of polarizabilities, and therefore Raman intensities, exhibit stronger basis set dependence and dispersion effects than the polarizabilities themselves. Whereas the calculated polarizabilities are very close to experiment, the agreement of their geometric derivatives and of the Raman scattering cross sections with experiment is less excellent. We attribute this mainly to the limitations of Placzek's theory (for Raman intensities) and to the low precision of the reference experimental data.