Ceilidh ... Re^4: H_eff in XMCQDPT

Firefly and PC GAMESS-related discussion club

Re^4: H_eff in XMCQDPT

>I think you simple math may work for supra-molecules containing
>several quasi-degenerate ligands. Take care to include all quasi-
>degenerated states into model space!

Certainly!

>You could opt for latest Firefly 8.0.0 beta which has improved XMCQDPT2 code.

Great! Is it possible to obtain 8.0.0 beta already?

>> As for the check of the overlap matrix of non-orthogonal eigenvectors, it's a good idea, thanks. So, if off-diagonal values are small and all eigenvalues of non-symmetric H_eff are real, it's no need to further increase H_eff, isn't it?
>No, the idea is that if they are large and/or some eigenvalues
>are complex, your XMCQDPT2 job is definitely running into problems.

What off-diagonal value should be considered as large: ~0.1, or ~0.01, or ~1? and is it safe if the imaginary part of an eigenvalue of non-symmetric H_eff is ~1.0e-16? And what should I do in case of problems? change some XMCQDPT parameters or start with another CASSCF solution?

>>By the way, in the next FF version, is it possible to print the WARNING that off-diagonal values are large or some eigenvalues of non-symmetric H_eff are complex?
>Is it too difficult to check this manually in the output? :)

For me, it is not difficult, but there are many less experienced FF users who knows nothing about possible problems. And I learned about this issue just now, in this discussion. Well, it may follow from your paper in J. Chem. Phys., but it is still in press and not available...

[ This message was edited on Thu Jun 2 '11 at 1:00am by the author ]

Thu Jun 2 '11 1:00am

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