Raman intensity calculations of formamide with the CNDO method

Within the polarizability theory, absolute and relative Raman scattering cross sections are calculated using a variational method and the finite field perturbation theory. The calculations are performed within the CNDO approximation and the basis set in the variational scheme is extended to include polarization functions. Satisfactory numerical results are obtained for the formamide molecule with the variational procedure. The FFP theory which was used up to now only for calculating relative Raman scattering cross sections is adequate in reproducing the relative values for formamide. The absolute scattering cross sections are too small. Because we are interested in calculations of biological relevant molecules, it is necessary to consider also the FFP method in the standard CNDO version, which is much more economical with respect to computer time and capacity than the variational method.