Application of time-dependent density functional response theory to Raman scattering

Recently, the first density functional theory (DFT) calculations on Raman intensities and depolarisation ratios were published. Those calculations were done in the static approximation. Here, we use time-dependent DFT in order to include the dependence of those properties on the frequency of the exciting light wave. By analytically calculating the frequency-dependent polarisability at different nuclear positions, our approach is closer to a fully analytic one than the previous DFT studies. Our results for five diatomics improve upon previous TDHF and SOPPA ab initio results and show that the frequency dependence cannot be ignored in quantitative comparisons to experiment. Our results for the important Q-branch differential Raman cross section of N2 are closer to the experimental value than previous results. Inclusion of the frequency dependence has little effect on the depolarisation ratios, but improves the results for the cross sections obtained in static DFT calculations. Our results obtained with three different exchange-correlation potentials yield similar results.