M1 transition moments


This might be a long shot, but is anyone aware if it’s possible/reasonable to extract magnetic (M1) dipole transition matrix elements from EOM-CC wavefunctions in Q-Chem? Do the transition densities between two EOM-CC states (in principle) provide sufficient information to compute M1 moments?

Phelan Yu

Hi Phelan,

Not completely, no:

  • The EOM-CC transition densities are available in the formatted checkpoint file if you use the rem variables cc_trans_prop = 2 and gui = 2.
  • To represent the magnetic dipole operator, you would need a dump of the angular momentum integrals, preferably in the atomic orbital basis. These are not available yet, but will be in the future.
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Hi Eric,

Got it – and thanks for the quick and succinct explanation.

For context, there’s some very early exploration being done in my (experimental) group about studying spin-flip/intercombination lines in small, optically active spin-orbit coupled molecules. Having the ability to model contributions from both SO intensity borrowing and higher order transition moments may be a nifty tool to have.

Looking forward to hearing updates on this in the future!

This is actually incorrect: angular momentum integrals for the EOM-CC/MP2 models have been available in Q-Chem for quite some time. The magnetic moments can be constructed from the printed properties in a post-processing step, for example, by modifying ezMagnet:
The ezMagnet code computes macroscopic magnetazabilities and magnetic susceptabilties from the ab initio data.

This paper describes the essential theoretical components and illustrates the Q-Chem capabilities by examples:

Hope this helps!

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Thanks, Anna! I will definitely take a look at the ezMagnet code.