[molpro-user] Computing higher roots in MRCI

[Garnet Chan]

Gerald is correct in that one can't target the "n" th eigenvector
directly, but, one CAN use the concept of Harmonic Ritz vectors to
obtain excited state eigenvalues near
a given input energy E without getting the other roots. You won't know
then if it's say the 6th or the 7th root, but you can
say it's the root closest to E. This is not implemented in Molpro
currently, but it would be simple to do so.

On Tue, Apr 14, 2009 at 9:49 AM, Gerald Knizia
<knizia at theochem.uni-stuttgart.de> 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.
> --
> Gerald Knizia
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