[molpro-user] MP2 pair energies

[Daniel Kats]

Dear Matthias

SCSFACS and SCSFACT correspond to coefficients for the opposite-spin and
same-spin energy contributions, respectively. You can get those from the
singlet/triplet contributions in the closed shell as
E_OS=E_singlet+(1/3)*E_triplet
E_SS=(2/3)*E_triplet

Best wishes
Daniel

On Wed, Dec 6, 2017 at 7:33 AM Matthias Heger <heger at ualberta.ca> wrote:

> I am a bit confused about the MP2 pair energies reported in my
> calculations. Specifically, my attached example yields:
>
> > SCS-MP2 correlation energy:           -0.198842375046   (PS=  1.200000
> PT=  0.333333)
> > (...)
> >  MP2 singlet pair energy              -0.126127623239
> >  MP2 triplet pair energy              -0.076321972220
>
> Scaling the pair energies manually and adding them yields a different
> energy (-0.176792... Hartree) than given above.
>
> In addition, I tricked the SCS calculation to only pick up the singlet or
> triplet pairs with SCSFACS and SCSFACT. That yields SCS correlation
> energies different from the corresponding pair energies in the output.
>
> Am I interpreting this wrong?
>
> Best,
> Matthias
>
> --
> Dr. Matthias Heger
> Department of Chemistry, University of Alberta
> 11227 Saskatchewan Drive NW
> Edmonton, AB T6G 2G2, Canada
>
> Office: CCIS 4-151
> Lab: CCIS 4-108
> Email: heger at ualberta.ca
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-- 
Daniel Kats
Institute for Theoretical Chemistry
University of Stuttgart
Pfaffenwaldring 55
D-70569 Stuttgart
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