Energy window / orbital selection in tddft

Hi all,

I am interested in calculating a subset of excitation energies in the x-ray region. I was guessing if it would be possible to restrict the energy range of the calculated tddft roots or even better restrict the MOs space in order to get only excitations from preset occupied MOs to a set of virtual ones. I could not find a suitable keyword/strategy in the manual to achieve this task.

Thank you for your support.


From my casual knowledge of TDDFT, I suspect that “restrict the energy range” isn’t theoretically possible.

“Restrict the MO space” sounds like core-valence separation, which is a common approximation for X-ray spectroscopy. Psi doesn’t support that. I think we all like the idea, but I don’t know of anybody who is committed to implementing it. (I’m the developer who has done the most work on TDDFT in the last couple years, and I’d rather support meta-TDDFT first.)

Thanks for the comment. Concerning the energy window, I recognize that my idea was not completely sound, and maybe I have used a misleading terminology. What I meant is indeed based on the selection of occupied MOs, whose energy is within the energy range. NwCHEM implements this feature through the EWIN keyword. Quoting NW manual:

" The EWIN keyword enables a restricted energy window between a lower energy cutoff and a higher energy cutoff. For example, ewin -20.0 -10.0 will only consider excitations from occupied orbitals within the specified energy window "

Ah, I thought you were talking about many-body energies - thanks for clarifying. Yes, that’s theoretically possible, we’d just need somebody to comment to implementing it.