Specifying spin for conical intersection optimizations?

qsimulate-open / bagel

Brilliantly Advanced General Electronic-structure Library

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Specifying spin for conical intersection optimizations? #220

Closed chertianser closed 3 years ago

chertianser commented 3 years ago

Hello,

I believe it is possible to obtain a CASPT2 optimized structure for the T1 state using the "nspin" tag, but I was wondering if it was possible to optimize a S0-T1 conical intersection (or any singlet-triplet CI) using CASPT2. As far as I can tell, the tags for "target" and "target2" only specify the number of the excited state, but contains no information related to "nspin".

Any help would be greatly appreciated!

shiozaki commented 3 years ago

Currently, there is no option that allows you to do this. Nuclear gradients for S0 and T1 can be computed separately -- that can be used to evaluate the gradient of average energies and energy differences; if you can use external geometry optimizer, you may be able to optimize for the minimum energy spin crossing point.