TDDFT calculations print out oscillator strength calculated by length form and velocity form. Which one should I compare with the oscillator strength printed out in eom-cc calculation?
The Oscillator strength values that you get from eom-cc in psi4 would be in length form.
Thank you very much!
BTW, just curious, anyone knows whether there is any conclusion that which form agrees with experiments better? I found many articles arguing which form is better before 80s. Any conclusion was made after that?
The conventional wisdom at one point was that the length form is “better” than velocity because the basis-set requirements for representing a derivative operator are more stringent. However, in my experience it really doesn’t matter very much, because one is typically only comparing oscillator strengths at a qualitative level, i.e. is a transition strong, weak, or non-existent? In that case, both forms give pretty much the same spectra for a given level of theory.