# [molpro-user] How to read the CSFs in a MRCI calculation?

José Cortés zolidus at gmail.com
Thu Aug 20 09:32:01 BST 2015

Dear Professor Knizia

Thank you very much for your reply. I have a question concerning the
coefficients of
the doubly external configurations.

My aim is obtain the CI vector in terms of determinants. I know this can
not be done
directly in the mrci module of Molpro, so I wrote a perl script.

I have no problems in the case of the reference function and simple
external configurations.
I can go from CSF to determinants by the genealogical coupling scheme.
However, this
is more difficult in the doubly external configurations case.

First, i transform each contracted configuration in terms of uncontracted
CSF´s

\Psi_{ijp}^{ab}=\frac{1}{2}(\hat{E}_{ai,bj}+p\hat{E}_{bi,aj})\Psi_{0}

=\sum_{P\nu}<\Psi_{ijp}^{ab}|\Psi_{P\nu}^{ab}>\Psi_{P\nu}^{ab}

where \Psi_{0} is the reference function (p=1 singlet coupling, p=-1
triplet coupling).
Then, I multiply each uncontracted CSF by the associated coefficient with
\Psi_{ijp}^{ab}
(listed in the output).  Later I express each uncontracted CSF in terms of
determinants.
As I understand it, the labels i, j, a, b, p in  \Psi_{ijp}^{ab} refer to
"I    J -> K    L     NP" in the output of Molpro.

However, performing this procedure does not achieve a square norm that
matches the output

CLASS          SQ.NORM        ECORR1        ECORR2
+++++++++++++++++++++++++++++++++++++++++++++++++++
Internals    0.00001717    0.00000000   -0.00000069
Singles      0.00065315   -0.00263386   -0.00263924
Pairs          * 0.00787253*   -0.03783725   -0.03783119

I do not understand that I'm doing wrong.
Perhaps, the coefficients associated with \Psi_{ijp}^{ab} are refer to a
non-orthonormal basis?
I would appreciate any help that you could provide me.

regards

Jose Jara