[molpro-user] Computing higher roots in MRCI

[Bernd Hartke]

Gerald Knizia wrote:
> On Friday 10 April 2009 21:12, Jaffe, Richard L. (ARC-TSN) wrote:
>> I am interested in computing the 6th root of B2 symmetry in non-linear C3.
>> I can determine the first 6 roots, but I am trying to reduce computational
>> cost by obtaining accurate solution only for the 6th root.
> 
> I don't know much about Molpros diagonalization routines, but from a purely 
> numerical standpoint I would guess that this is impossible. I'm not aware of 
> any matrix diagonalization algorithm that can calculate a specific 
> eigenvector without also calculating all lower (or all higher) ones.
>
you may want to check out things like "inverse iteration" or "filter
diagonalization" etc.

Best regards,
Bernd Hartke

---
Prof. Dr. Bernd Hartke             e-mail: hartke at phc.uni-kiel.de
Theoretical Chemistry              phone : +49-431-880-2753
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