Subject: 2-Density Matrix

From: Xavier Fradera i Llinàs <[email-masked]>
Date: Thu, 14 Nov 1996 12:10:19 +0000

Dear CCLers,
we are interested in getting 2nd-order density matrices from Gaussian-94
outputs, at different levels of theory (HF, MP2, CI ...). We have tried
to obtain them from link L1111, i.e.:

#HF 3-21G iop(11/33=4,11/28=-1) extralink=(L1111) pop=full

#MP2 3-21G FREQ iop(11/33=3)

This way, the program lists an "AO 2PDM", which doesn't integrate to N(N+1)/2,
excepting HF with H and He (only s functions). For atoms having p functions,
the read HF 2PDM doesn't coincide with the one computed from the 1PDM, in
spite of taking into account the (2-delta(ij))(2-delta(kl)) factors. At MP2
and CI levels we have never obtained "good" 2PDMs. This makes us question
whether this is really the 2PDM matrix or not, unless there are other kind
of factors we are not considering.

So, we have these questions:

1.- Why does HF 2PDM work when only s functions are present ? Can there be
any problem when p functions are added ?

2.- At MP2, CI levels, are we really getting the 2PDM matrix from L1111 ?
If not, is it possible to obtain it from other links ?

Thank you in advance for any help.

------------------------------------------------------------------------------
Xavier Fradera        [email-masked]
Maricel Torrent       [email-masked]
Institute of Computational Chemistry - University of Girona - CATALONIA
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     /-------------------------------------------------------/
    / Xavier Fradera i Llinàs - IQC - Universitat de Girona /
   / E-mail: [email-masked]                           /
  /-------------------------------------------------------/