[molpro-user] relaxed Pople cluster corrections

[Andy May]

A bug report has been made about this problem by Prof. Werner here:

https://www.molpro.net/bugzilla/show_bug.cgi?id=3937

Best wishes,

Andy

On 14/12/12 16:19, harding wrote:
>   I believe the relaxed Pople cluster corrections coming out of Molpro
> are incorrect.
>
>   If I do the following calculation using Molpro 2010.1 :
>
> memory,20,m
> geometry={
>   C }
>
> basis=vtz
>
> {multi
> occ,2,1,1,0,1,0,0,0
> closed,1,0,0,0,0,0,0,0
> wf,6,4,2}
>
> {ci}
>
> I get the following results:
>
>   Coefficient of reference function:   C(0) = 0.98244004 (fixed)
> 0.98247737 (relaxed)
>   Reference energy                     -37.70568461
>   Correlation energy                    -0.07384460
>   !MRCI STATE 1.4 Energy               -37.779529217128
>
>   Cluster corrected energies           -37.78219258 (Davidson, fixed
> reference)
>   Cluster corrected energies           -37.78218676 (Davidson, relaxed
> reference)
>
>   Cluster corrected energies           -37.78086047 (Pople, fixed
> reference)
>   Cluster corrected energies           -37.77952922 (Pople, relaxed
> reference)
>
>   Note that the relaxed Pople cluster corrected energy is identical to
> the uncorrected CI energy.
>
>   I can reproduce the fixed and relaxed Davidson results using the
> equations in section 20.7 of the Molpro manual. As an aside I note that
> there appears to be a numbering inconsistency in the manual as the
> equation numbers in Table 9 do not correspond to those in the text.
>
> I can reproduce the fixed Pople correction using equation 65 from Pople,
> Seeger and Krishnan IJQC, s11, 149 (1977) with n=4. If I use the same
> equation and just replace the fixed C0 with the relaxed C0 listed above
> I get a relaxed Pople cluster corrected energy of,
>
> -37.78085755
>
> not the value shown above.
>
> Am I doing something wrong here or is Molpro in error ?
>
> Larry Harding
>
>
>
>
>
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