TD-DFT: Ordering of excited states

Hi everyone,

We are currently attempting to do a TD-DFT scan for a molecule and examining the energy of each of the excited states as a function of the bond distance. While Q-Chem print the states in order of energy, there are a great number of crossings within the constraints of the scan. Is there a way to have the program print the states in a manner such that the state 1 always corresponds to a certain state, state 2 always corresponds to another one, etc., despite the ordering of the energies throughout the scan?

Thank you!

NOPE! This is a fun feature of Born-Oppenheimer quantum chemistry, you get states in energetic order because that is how they come out of the eigenvalue problem.

There is a state-tracking algorithm based on attach/detach densities (see manual – I have not used and I’m not 100% sure it’s appropriate to this issue). Alternatively, looking at Natural Transition Orbitals can help you figure out what state is what, but you have to do it manually. CIS_AMPL_ANAL=TRUE will give you NTOs and various other additional information.

This is a “feature” (of the physics), not a bug.