Is it possible to use the NTO-rotated orbitals (for a specific TDDFT state) as the MO set in a subsequent Q-Chem job?

Questions
#1

Hi all,

I’m running TD-DFT absorption spectra in Q-Chem and I’d like to test the following idea:

For a specific excited state (say state n), I compute its Natural Transition Orbitals (NTOs). Then, I want to take the rotated MO set from that NTO analysis and use it as the MO basis in a subsequent Q-Chem job, to see whether the computed transition dipole moment oscillator strength for that same state is improved when the excitation is recomputed in that rotated orbital representation.

Concretely, my intended workflow is:

  1. Job A: run ground-state SCF + TDDFT, request NTO analysis for a target root.
  2. Export/save the MO coefficients corresponding to the NTO-rotated orbitals (or some orbital file containing them).
  3. Job B: restart from those orbitals (i.e., force Q-Chem to use that orbital set), skip the SCF and recompute TDDFT excitations.

My questions:

  1. Is it actually possible in Q-Chem to export the NTO-rotated orbitals as a reusable “MO set” for a later job? (i.e., not just printing NTOs for visualization, but generating a restartable orbital coefficient set that Q-Chem can read back in.)
  2. If yes: what is the recommended way to do it?

Please let me know if information from my side is most useful to follow-up in scientific discussion.

Thanks a lot!

#2

I think this can probably be accomplished but it’s not push-button (i.e., there’s no single $rem variable to do this). What you can do is to generate NTOs in MolDen format, for a particular excited state (instructions are in the manual). Then, you may be able to use a tool such as MOkit to transform those into a format that is appropriate to be read in as guess MOs for a subsequent Q-Chem job.

There’s a sample job that describes the first step, the relevant part of the input is:

$rem
method          pbe0
basis           6-31+G*
scf_guess       read
print_orbitals  true
molden_format   true    ! get the NTO coefficients in Molden format
make_cube_files ntos    ! generate cube files of the NTOs...
cubefile_state  2       ! ...for the 2nd excited state
$end
#3

Dear John, thank you for the ready reply. I will look more carefully into the options I have with MOkit and see if I can produce a MO file for Q-Chem. Best wishes for the end of 2025 and a happy 2026!