I am doing calculation to see excited state and ground state raman intensities. I have successfully done it for ground state using dft and after finding absorption wavelength , have optimized the geometry at the excited state .
1) So should I calculate the raman frequencies at the point in excited state using td-dft with same geometry as ground state or should I allow it to go to its optimized excited state geometry and then do my calculation?
2) What is static and pre-resonance Raman and how do they differ ?
3) What are the keywords , I need to focus on here. I have tried adding a freq=raman along with the numerical frequency calculation . But this came out with a unrecognized frequency type error.
Can someone please suggest an answer to my queries.
G09 doesn't directly support Raman calculation for excited state. Raman task for excited state at TDDFT and CIS level is available since G16 B.01.
Pre-resonance Raman corresponds to the case that frequency of incident light is close to electronic excitation energy, which can be determined by excited state calculation prior to pre-resonance Raman calculation.
Thank you for your reply first of all .
So I have found that my absorption energy is close to the Frequency of incident light . Now what information does this pre-resonance Raman provide me ? Is this a ground state or excited state calculation and is this too limited to Gaussian 16 ?
If the incident light frequency specified in "freq=raman CPHF=rdfreq" calculation for ground state is close to the excitation energy calculated by TDDFT using same functional and basis set, the resulting Raman activity will correspond to pre-resonance Raman case, this task can be done by both G09 and G16. (Note that "pre-resonance Raman" is very different to Raman of excited state).
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