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Re^2: H_eff in XMCQDPT

sanya
sanya@photonics.ru

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). 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 Heff :) 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?

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?

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 Heff and check
>how stable the transition energies of interest are. Another
>thing to check is the overlap matrix of non-orthogonal
>eigenvectors corresponding to Heff before symmetrization.
>There should not be large off-diagonal values here, and
>all eigenvalues of non-symmetric Heff 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?

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