State Specific (Mk) MRCC Availability

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1 year 4 weeks ago #993 by ghjones
Hello,

I was looking through the manual at the options for multireference coupled cluster calculations, and noted that the default (or perhaps only?) ansatz was the "multireference inspired" SR-MRCCSD, if I parsed the acronym and references correctly.

It was mentioned in "Full implementation and benchmark studies of Mukherjee’s state-specific multireference coupled-cluster ansatz" J. Chem. Phys. 132, 074103 (2010) that an implementation of the Mk-MRCC might become available in the MRCC package, and I was wondering if that implementation was available to the public. It's quite possible I missed a keyword somewhere in the manual.

I ask about the availability, as the problem I'm trying to solve involves multiple stationary points of significant multireference character, but among these points there doesn't appear to be an obvious consistent choice of Fermi vacuum for a SR-MRCC. One approach I was considering was a localized orbital Mk-MRCCSD approach, but all the implementations of the Mk formalism I've found require a difference of no more than 2 excitations between any two reference determinants, which isn't fulfilled for my minimal CAS(4,4).

Any input, either with respect to the availability of Mk-MRCC or general advice on the problem, would be greatly appreciated.

Kind regards,
Greg

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1 year 4 weeks ago #994 by kallay
Dear Greg,
Mk-MRCC is not available in the public release. SR-MRCC is the only option.

Best regards,
Mihaly Kallay

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1 year 4 weeks ago #995 by ghjones
Thank you so much for the quick response! I will investigate other approaches.

Best,
Greg

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