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

 Sent to CCL by: "Johannes Hachmann" [jh388(0)cornell.edu]
 Hi John,
 obviously you are usually interested in the proper electronic ground state - but
 being interested in e.g. spin gaps, or a comparison of the electronic
 structure/orbital sets of different spin states, or in a specific starting guess
 for a post-HF calculation (which happens to be not the ground state) is not that
 far fetched... Then it doesn't really help you if your calc always falls back on
 the ground state which has a symmetry that's not of interest for you.
 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(0)ccl.net
 > [mailto:owner-chemistry+jh388==cornell.edu(0)ccl.net] On
 Behalf
 > Of John McKelvey jmmckel__gmail.com
 > Sent: Thursday, March 05, 2009 12:12 PM
 > To: Hachmann, Johannes
 > Subject: CCL:G: G- How to retain the symmetry in a SCF calculation ?
 >
 > Is the possibility of finding a symmetry of lower energy _all
 > that bad_?  I can think of an obvious reason why it would be
 > beneficial....
 >
 > Cheers,
 >
 > John McKelvey
 >
 >
 >
 > On Wed, Mar 4, 2009 at 11:19 PM, Johannes Hachmann jh388 ~~
 > cornell.edu <owner-chemistry(0)ccl.net> wrote:
 >
 >
 >
 > 	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
 > <mailto:owner-chemistry%2Bjh388> ==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
 > <mailto:owner-chemistry%2Bjh388> ==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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