Subject: SUMMARY size-consistent AND variational

From: elewars <[email-masked]>
Date: Sat, 07 Sep 2002 18:08:48 -0400

2002 Sept 7

SUMMARY of answers; I am sory if I have omitted anyone. I thank all who
responded.
EL

Question
2002 Aug 25

Hello,

Does anyone know of a method (correlation level, like HF, MP, CI,
CASSCF, etc.) besides HF and full CI that is both size consistent AND
variational?

Thanks.

E. Lewars
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Answers
#1(a)
This ref. might be of interest:
  A.I. Krylov, "Spin-flip configuration interaction: an electronic
  structure model that is both variational and size-consistent",
  Chem.Phys.Lett. 350 (2001) 522-530

Have a nice day,
    Mikael J.
    http://www.chem.helsinki.fi/~mpjohans/

 1(b)
[...what do you think about CASSCF and size consistency?...]

I don't know that much about CASSCF, but I would think it is
size-consistent, at least if the active space is chosen properly. But
don't
take my word for it :-)

Have a nice day,
    Mikael J.
    http://www.helsinki.fi/~mpjohans/

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#2
Dear Dr. Lewars,

Variational in the sense of being an extremum of some functional are the

coupled-pair-functional (CPF) and the averaged coupled pair functional
(ACPF) from the Ahlrichs group. These methods are also nearly size
consistent. However, the energies they give are not an upper bound to
the
lowest eigenvalue of the Hamiltonian (they are bounded from below
though).

Recently Anna Krylov has published some papers on "spin flip CI" in JCP
and
CPL. This method is, for a restricted set of problems, both,
size-consistent and variational. It has other shortcomings but I enjoyed

the general idea because its is simple and appealing.

Apart from that nothing pops up at first glance; please let me know if
you
get interesting responses!

Hope that helps,

best regards,
Frank

___________________________________________________________________________

  PD Dr. Frank Neese                      Tel. +49-208-306-3657
  Max Planck Institut für Strahlenchemie  E-mail:
[email-masked]
  Stiftstr. 34-36
  Mülheim an der Ruhr
  Germany

  http://www.mpi-muelheim.mpg.de/strneu/index_e.htm
___________________________________________________________________________

#3
Spin-unrestricted geminal theory based on strongly orthogonal geminals.
Its general (not necessary size consistent) form is known as SEP or
APSG,
see P. Surjan in Topics in Current Chemistry, vol. 203, pp 63-88 for
review.  The rigorously size consistent form is SSG, see V. Rassolov,
JCP,
in print (Oct. 2002). I can send you a preprint if you're really
interested.

Vitaly Rassolov
Dept. of Chemistry and Biochemistry         (803) 777-7811
University of South Carolina            fax (803) 777-9521
631 Sumter St
Columbia, SC 29208
[email-masked]
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#4
ACPF or AQCC may be close to what you are looking for.

Galina

------------------------------------
Dr. Galina Chaban
NASA Ames Research Center
Mail Stop T27B-1
Moffett Field, CA 94035-1000
Tel (650) 604-4995
Fax (650) 604-1095
e-mail: [email-masked]
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#5

"Van Dam, HJJ (Huub)" <[email-masked]>

CASSCF should be provided that you choose your active orbitals
correctly.
DFT should be size consistent as well. That's it...

Huub van Dam
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