More or less, you start with a quantum chemical DFT calculation, the Raman frequencies are associated with the vibrations of the molecule (second derivatives of the energy, once you're at the relaxed potential energy state). Raman frequencies are shifts (Stokes and anti-Stokes) relative to the laser frequency.
For medium sized molecule, a hybrid DFT calculation (which scales in computational time with N_eletrons^3 ) would cost a few CPU days of time, giving pretty accurate frequencies (there are known correction factors of ~0.95x to compensate for systematic failings in the theories).
What we are very bad at is predicting the Raman intensity from theory.
But you get the frequencies in the correct order, and can use this to assign observed peaks to particular vibrations within the molecule.
For medium sized molecule, a hybrid DFT calculation (which scales in computational time with N_eletrons^3 ) would cost a few CPU days of time, giving pretty accurate frequencies (there are known correction factors of ~0.95x to compensate for systematic failings in the theories). What we are very bad at is predicting the Raman intensity from theory. But you get the frequencies in the correct order, and can use this to assign observed peaks to particular vibrations within the molecule.
http://www.gaussian.com/g_tech/g_ur/k_freq.htm