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Alex Granovsky

gran@classic.chem.msu.su

Dear Sanya,

>Thank you very much. Actually, I'm currently dealing with homo- and heteroleptic metal complexes, where several quasidegenerate excited state of the same nature are possible (say, excitations involving Ligand1, Ligand2, and Ligand3).

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!

> The systems have up to 1000 basis functions, and each XMCQDPT2 calculation takes up to 3-4 days on a quad-core PC (and a lot of disk I/O). So, it is not easy to experiment with increasing dimension of H_{eff} :)

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

> 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.

>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? :)

Cheers,

Alex

>On Tue May 31 '11 9:34pm, Alex Granovsky wrote

>----------------------------------------------

>>Dear Sanya,

>>I'm afraid XMCQDPT2 with dimension of model space equal

>>to ca. 30-50 as you suggest will be prone to intruder

>>state problem. I'd not use more than ca. 20 states for

>>organic pi-systems. Unfortunately there are no general

>>recipe here. You can try to perform several calculations

>>with increasing dimension of H_{eff} and check

>>how stable the transition energies of interest are. Another

>>thing to check is the overlap matrix of non-orthogonal

>>eigenvectors corresponding to H_{eff} before symmetrization.

>>There should not be large off-diagonal values here, and

>>all eigenvalues of non-symmetric H_{eff} must be

>>real numbers.

>>Cheers,

>>Alex

>>

>>

>>On Sun May 29 '11 5:11pm, sanya wrote

>>-------------------------------------

>>>How to estimate the size of H_eff in XMCQDPT (nstate or kstate keys)? I know that for 1 excited state H_eff of 10-12 states is enough, but typically I need 3-4 excited states. Does this proportion keeps for higher-lying states?

Wed Jun 1 '11 7:00pm

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