>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 Heff are real, it's no need to further increase Heff, 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 Heff 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 Heff 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 ]