# CCL:G: G- How to retain the symmetry in a SCF calculation ?

• From: "Johannes Hachmann" <jh388 a cornell.edu>
• Subject: CCL:G: G- How to retain the symmetry in a SCF calculation ?
• Date: Wed, 4 Mar 2009 23:19:24 -0500

``` Sent to CCL by: "Johannes Hachmann" [jh388_._cornell.edu]
Hi Ding,
sorry, never ran into this problem. Note that you might have to try a number of
orbital swaps to get to the wavefunction irrep you want. Also, in case you use
the STABLE keyword, DO NOT use STABLE=OPT because that will likely bring you
back to a more stable wavefunction of different symmetry.
Hope that helps
Best
Johannes
---------------------------------------------------------------
Johannes Hachmann
(Dipl.-Chem., M.Sc.)
Chan Research Group
140D Baker Laboratory
Department of Chemistry and Chemical Biology
Cornell University
Ithaca, NY 14853-1301
USA
---------------------------------------------------------------
> -----Original Message-----
> From: owner-chemistry+jh388==cornell.edu[-]ccl.net
> [mailto:owner-chemistry+jh388==cornell.edu[-]ccl.net] On Behalf
> Of xunlei ding dingxunlei:_:gmail.com
> Sent: Wednesday, March 04, 2009 5:12 AM
> To: Hachmann, Johannes
> Subject: CCL:G: G- How to retain the symmetry in a SCF calculation ?
>
>
> Sent to CCL by: xunlei ding [dingxunlei|gmail.com] Dear Johannes,
>
> Sometimes scf=QC works but not always.
> I hope there be a better way for this problem.
>
> It seems that we can use IOP, as is described as:
>
> IOp(5/15)
> Apply Abelian symmetry constraints on orbitals.
>
> 0        Default (1 for L502, 2 for L501 and L506).
> 1        No.
> 2        Yes, keep occupation of each irrep the same as the
> initial guess.
> 3        Yes, keep overall wavefunction the same as the initial guess,
> but doing the minimal amount
>          of orbital switching to accomplish this.
> 00       Default (use Abelian symmetry in diagonalization).
> 10       Use Abelian symmetry in diagonalization.
> 20       Do not use Abelian symmetry in diagonalization.
>
> But in my test, iop(5/15=2) doesn't work.
>
> Any more suggestions?
>
> Thanks a lot!
>
> Best regards,
> Ding
>
>
>
> 2009/2/13 Johannes Hachmann jh388[*]cornell.edu
> <owner-chemistry||ccl.net>:
> >
> > Sent to CCL by: "Johannes Hachmann" [jh388!A!cornell.edu] Hi
Ding,
> >
> > use SCF=QC (however quadratically convergent SCF is a bit
> costy...).
> > See description under
> http://www.gaussian.com/g_ur/k_guess.htm on the
> > bottom together with GUESS=ALTER. This is not a
> particularly elegant
> > way to do things (compared to just specifying the state symmetry in
> > e.g. MOLPRO) but it works. You might want to use the STABLE
> option so
> > that you know whether you have instabilities to which other
> states and
> > which additional MO swaps you might want to perform.
> >
> > Best
> >
> > Johannes
> >
> > ---------------------------------------------------------------
> > Johannes Hachmann
> > (Dipl.-Chem., M.Sc.)
> >
> > Chan Research Group
> > 140D Baker Laboratory
> > Department of Chemistry and Chemical Biology Cornell University
> > Ithaca, NY 14853-1301 USA
> > ---------------------------------------------------------------
> >> -----Original Message-----
> >> From: owner-chemistry+jh388==cornell.edu[]ccl.net
> >> [mailto:owner-chemistry+jh388==cornell.edu[]ccl.net] On Behalf Of
> >> xunlei ding dingxunlei::gmail.com
> >> Sent: Friday, February 13, 2009 3:42 AM
> >> To: Hachmann, Johannes
> >> Subject: CCL:G: G- How to retain the symmetry in a SCF
> calculation ?
> >>
> >>
> >> Sent to CCL by: xunlei ding [dingxunlei.:.gmail.com] Dear CCLers,
> >>
> >> In the manual of G03, the key word "SCF= Symm" is
> discribed as below:
> >> Retain all symmetry constraints: make the number of
> occupied orbitals
> >> of each symmetry type (abelian irreducible
> >> representation) match that of the initial guess. Use this
> option to
> >> retain a specific state of the wavefunction throughout the
> >> calculation. It is the default only for GVB calculations.
> >>
> >> But sometimes it doesn't work and the last state is different from
> >> the initial state.
> >>
> >> Could you give me more suggestions on how to retain the
> symmetry in a
> >> SCF calculation?
> >>
> >> Thanks!
> >>
> >> Best regards,
> >> Ding
> >>
> >>
> >>
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>
> --
> ------------------------------------------------------
> Xun-Lei Ding
> Associate Research Professor of Physical Chemistry State Key
> Lab for Struct. Chem. of Unstable and Stable Species
> Institute of Chemistry, The Chinese Academy of Sciences
> Zhongguancun North First Street 2，
> Beijing 100190, P. R. China
> Phone 86-10-62568330
> Fax   86-10-62559373
>
>
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