[molpro-user] Computing higher roots in MRCI

[Tatiana Korona]

Hi, Gerald,

In the Davidson diagonalization routine you can lock on a specific vector, 
i.e. you can calculate the nth vector without optimizing the lower n-1. 
You should keep of course the lower vectors in the P space, but you update 
only the desired one(s). You are however, not guaranteed to converge to 
the right answer (sometimes the diagonalization routine can "lock" on a 
wrong root, which at the first iteration happens to be the nth one, but 
after some optimizing would change its place). I programmed such algorithm 
once for EOM-CCSD, but the question remains how to do the same for MRCI.

Best wishes,

Tatiana


  On Tue, 14 Apr 2009, 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.
> -- 
> Gerald Knizia
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Dr. Tatiana Korona http://tiger.chem.uw.edu.pl/staff/tania/index.html
Quantum Chemistry Laboratory
University of Warsaw
Pasteura 1, PL-02-093 Warsaw, POLAND


`The man who makes no mistakes does not usually make anything.'
                                        Edward John Phelps (1822-1900)