SOC matrix element between high multiplicities

[manishrana]

Dear users and developers,

I want to calculate the SOC matrix elements between quintet and septet spin multiplicities. But on this forum, I have only seen discussion on SOC matrix elements between singlet and triplet. Can I calculate the SOC matrix elements between higher spin multiplicities in Dalton?

Thanks

[taylor]

The spin-orbit operator can be thought of as having the action DeltaS = +/-1 when operating on a given wave function. If that wave function has S=0 then there is only one result: DeltaS=+1 (so singlet/triplet coupling). If you operate on a wave function with S other than zero (or 1/2) you can get results from DeltaS=+1 and DeltaS=-1. So if you operate on quintets you can get triplets and septets. As long as you are comfortable sorting through the results of the response calculation and identifying which final states are which it should be possible to do what you want.

Be aware that the only computational level that can be used for this is MCSCF. There are no methods in Dalton for including both spin-orbit and dynamical correlation for open-shell states that I am aware of. One could perhaps use open-shell DFT but I would be very sceptical of the quality of the results because the target quantities would not have been used in parametrizing the functional.

Best regards
Pete

[olav]

Theoretically you can only do this with Dalton in the context of a CI response calculation, assuming e.g. that you have a converged quintet reference state and run a CI linear response with (frozen orbital) calculation on top of that, plus, you would have to manually analyse the multiplicity of the excited states based on their determinant expansions. If the question is if there is an input option to accomplish this in a black-box manner, the answer is no.

Regards,
Olav