Calculation Of Raman Intensities
Raman intensities can be evaluated in a computation of a harmonic force field (keyword VIB=ANALYTIC) by specifying in addition RAMAN_INT=ON or RAMAN_INT=DYN. In the first case, the calculation is based on the geometrical derivative of the static polarizability tensor, while in the second case the derivative of the dynamical polarizability is computed.
At the CC level, all calculations have to be carried without orbital relaxation with respect to the electrical-field perturbations included (keyword RAMAN_ORB=UNRELAXED), while at the HF-SCF level orbital-relaxation necessarily has to be included (RAMAN_ORB=RELAXED).
Note that a frequency (within a %frequency section) has to be given when differentiating the dynamical polarizability tensor.