## Firefly and PC GAMESS-related discussion club

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Re^4: MCSCF for a large system.
Dear Sanya,
Thanks for the comment. To be honest the voluntarism is what makes me really upset - if you have two different mcscfs converged, which one is (more) trustworthy and why? I can explain only orbital selection part of the the problem - the difference is due to limited active space and better understanding/bigger size of the active space would be more accurate. But what is about nstate? I have plenty of states very close at energy scale and I am not sure that in active site of my protein the amount of excited substrate is say 0.28 or 0.5 under thermal pressure of the surrounding protein body. It can be next to zero and just waiting for kinetic energy to be focused by protein body for example, why not? Intuitively I would join reaction path/coordinate to states weight selection because for reasonably selected active space only certain route of weights increasing for desired states is leading toward the reaction products. So can you please give some insights of why do you think that ignoring of the reaction coordinate and setting states on/off is the best strategy?
Thanks for the suggestion - I'll check aldet vs guga performance.
Thanks,
Alex

On Sat Sep 27 '14 8:35pm, sanya wrote
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>I agree with Ilya: the choice of active space and state-averaging scheme is mostly a matter of trial-and-error and experience. Using localized and properly reordered orbitals may help to reduce the active space.

>By the way, I recommend using cistep=aldet option (\$DET group is used in this case instead of \$DRT), which is better parallelized. If you need to average the states of only one multiplicity, set pures=.t. In this case, you may set ispin to 0 or 1, depending on which multiplicity (odd or even) you need. Don't forget to adjust NSTGSS to 3*NSTATE. If different multiplicities should be averaged, set pures=.f.

>Playing with fractional weights in wstate is not a good idea. Actually, fractional weights are used in very special cases. Just set 1 if you want to include the state in the averaging or 0 to exclude it.

Sun Sep 28 '14 1:25am