DIIS failed to converge for QMMM and QC-SCF is not implement

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Stine
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First name(s): Stine
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DIIS failed to converge for QMMM and QC-SCF is not implement

Post by Stine » 15 Apr 2014, 11:43

Hi

I am running QM/MM calculations for a system where a molecule (QM) is placed between two clusters of metal (MM), which is working fine. However, when I am trying to take a few of the metal atoms from the cluster and including them in the QM part I get the following message after a few hours:

DIIS failed to converge for QMMM and QC-SCF is not implemented for QMMM

Is there a way to handle this issue?

Best regards
Stine

kennethruud
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Re: DIIS failed to converge for QMMM and QC-SCF is not imple

Post by kennethruud » 15 Apr 2014, 11:50

Well, not sure there is a unique solution, but to avoid the last step, where the calculation crashes because the quadratically-convergent scheme has not been implemented, used

.NOQCSCF

in the *SCF INPUT module.

However, you will still need to play around with getting the DIIS to converge. You can here play with level shifting, different starting guesses, try to restart from a state that you for some reason think is better than the regular starting guesses (but without including the previous DIIS information). I believe the manual (as well as the archives) gives some suggestions on how to proceed with making a poorly convergent SCF state converge.


Best regards and good luck!

Kenneth

Stine
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Country: Denmark

Re: DIIS failed to converge for QMMM and QC-SCF is not imple

Post by Stine » 15 Apr 2014, 12:32

Thanks, I will try that :)

erik
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Re: DIIS failed to converge for QMMM and QC-SCF is not imple

Post by erik » 15 Apr 2014, 12:58

Hi Stine

As Kenneth suggested, turning of QC could solve you convergence problem, but the fact that you even run into convergence problems, might already indicate that you need a quadratic convergent solver. We implemented this for QM/MM in relation to PE/MCSCF (http://scitation.aip.org/content/aip/jo ... /1.4811835), but it is not an official part of the release. However, if you want to do a double check of you converged result from DIIS (if it converges) or simply need the quadratic convergent part, then we could set up a DALTON where the neccesary stuff is there (located where you like, if I can get access there somehow...). It would however, require that me and Jacob are involved in the project. Let me know if you are interested...

Personally, I would certainly check the results with QC if possible if the DIIS runs into trouble. The DIIS procedures are not always stable (!) - especially not for more challenging molecules like open shell systems etc...

-Erik

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