There are a few things about VSCF that I don't understand:

  1. Which coordinates do you work in? If you work in normal mode coordinates, how do you evaluate the effect of the average of one normal mode on another one, with a different normal mode coordinate? Why can't you just work in Cartesian coordinates?
  2. Unlike the electronic SCF, the total number of vibrational quanta is not fixed for a particular molecule. How do you select which modes to include in your 'mean field'? Do you assume that all vibrational modes have only one quanta of energy in them?
  3. At the end of VSCF, how easily could you go from the resulting set of vibrational modes described in terms of atomic movement to a vibrational wavefunction? E.g. a one that one could you to directly evaluate a Franck-Condon integral $\langle\psi^{\text{vib}}_0|\psi^{\text{vib}}_1\rangle$?

I feel like I have a lot of misunderstanding here, so I'd be grateful if you could bear with me and give as much detail as possible.


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