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

 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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