[molpro-user] How to read the CSFs in a MRCI calculation?
Gerald Knizia
knizia at theochem.uni-stuttgart.de
Wed Aug 12 18:15:30 BST 2015
Dear José,
you are right about \ and / indicating spin couplings in the
geneological coupling scheme. Regarding the doubly external
configurations: These are not individual CSFs, but they indicate
internally contracted configurations, in which spin-free excitation
operators are applied to the entire reference function:
|Phi^ij_ab> = E^{ab}_{ij} |Phi>
with |Phi> being the full MCSCF-type reference function (not individual
CSFs), i and j being occupied orbital labels, and a and b being external
orbitals.
The operator E^{ab}_{ij} denotes explicitly
E^{ab}_{ij} = \sum_{\sigma \in A,B} \sum_{\tau \in A,B} c^{a \sigma}
c^{b \tau} c_{j \tau} c_{i \sigma}
where \sigma and \tau sum over spin labels.
Best wishes,
Gerald
On Sun, 2015-08-09 at 21:51 -0500, José Cortés wrote:
> Dear molpro users
>
> I have a question about the output of the CSFs in a mrci calculation.
> As an example suppose the He2 molecule with the 6-311G basis,
> where an active space of 4e,4o was chosen in the part of the casscf
> calculation.
> Such election leaves only two external orbitals. As I understand the
> symbols
> "/" and "\" concerning to relative spin couplings, which are related
> to the t vectors
> in the genealogical coupling scheme.
>
> For example for the following configurations (which are in the output
> of the MRCI calculation)
>
> Reference coefficients greater than 0.0000000
> ================================
> 2200 0.9959538
> /\/\ 0.0600897
>
> Coefficients of singly external configurations greater than
> 0.0000000
> ================================================
> /\\0 5.1 -0.0062116
> 20\0 6.1 -0.0055316
>
> the t vectors specified in the complete basis set would be like:
> 220000
> /\/\00
> /\\0/0
> 20\00/
>
> However, my question arises in the doubly external configurations
>
> Coefficients of doubly external configurations greater than
> 0.0000
> ===========================================
> PAIR I J -> K L NP SYM REF
> COEFFICIENTS
> 4 2.1 2.1 5.1 5.1 1 1 1 -0.02645858
> 1 1.1 1.1 5.1 5.1 1 1 1 -0.02035037
> 4 2.1 2.1 6.1 6.1 1 1 1 -0.01367284
> 9 3.1 3.1 5.1 5.1 1 1 1 -0.01342122
>
> In this case, how the t-vectors should be specified for each one of
> the configurations in the complete basis set?
> How do I get in this case each one of the configurations?
> I would appreciate any information you could give me about it.
>
> Regards
> José Jara
> Universidad Nacional
> Autónoma de México
>
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