| 10:15:50 AM PDT - Wed, Jul 9th 2014 |
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Hi,
NWChem supports analytical DFT frequencies for closed shell and unrestricted open shell calculations. There are some additional limitations due to the requirement for 2nd order partial derivatives of the functional you are using. At the moment we don't have these for all functionals but I hope to have that problem fixed soon.
For RODFT the story is a bit different as there is an additional constraint (additional relative to unrestricted open shell) that the alpha and beta orbitals should be the same. This leads to an additional Lagrangian in the gradient expression with has been coded in NWChem. But we haven't worked out what this additional term means for the frequency calculations. So, you are right that if you do an RODFT frequency calculation then the 2nd derivative will be constructed by numerically differentiating the gradient.
Huub
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