## Firefly and PC GAMESS-related discussion club

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** Re^4: H_eff in XMCQDPT **
sanya

sanya@photonics.ru

>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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