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compas / grasp

General Relativistic Atomic Structure Package
https://compas.github.io/grasp/
MIT License
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rcsfinteract triple excitations #99

Open mkkarlsen opened 1 year ago

mkkarlsen commented 1 year ago

Hi.

I am trying to expand a calculation to include triple excitations.

rcsfinteract seems to remove all CSFs corresponding to such excitations.

I think it is not very feasible to run without rcsfinteract as the number of CSFs increases very rapidly with SDT excitations.

Any ideas what I am missing here?

Thank you. Martin

tspejo commented 1 year ago

Hi Martin,

Yes, rcsfinteract keeps all CSFs that interacts with CSFs in the multireference.

If you have only one CSF in the MR you will get CSFs that interacts with this single CSFs. Since the interaction is described by one- and two-body interactions, the CSFs you get from rcsfinteract can never differ by more than two electrons from the CSFs in the MR (so you effectively remove all CSFs that results from triple excitations).

Yes, the expansion grows very rapidly when including triple excitations. An alternative approach would be to include only single and double excitations, but make the MR larger. Just a suggestion.

Best wishes Per

From: mkkarlsen @.> Sent: Thursday, January 19, 2023 9:54 AM To: compas/grasp @.> Cc: Subscribed @.***> Subject: [compas/grasp] rcsfinteract triple excitations (Issue #99)

Hi.

I am trying to expand a calculation to include triple excitations.

rcsfinteract seems to remove all CSFs corresponding to such excitations.

I think it is not very feasible to run without rcsfinteract as the number of CSFs increases very rapidly with SDT excitations.

Any ideas what I am missing here?

Thank you. Martin

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mkkarlsen commented 1 year ago

I see.

Thank you.