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Subject: RE: [NWCHEM] turn off symmetry
Date: Mon, 19 Feb 2007 12:46:45 -0800
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Thread-Topic: [NWCHEM] turn off symmetry
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From: "Vorpagel, Erich R" <Erich.Vorpagel@pnl.gov>
To: "Van Dam, HJJ \(Huub\)" <h.j.j.vandam@dl.ac.uk>,
        "simon" <spierre@few.vu.nl>, <nwchem-users@emsl.pnl.gov>
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Greetings Simon,

Another way to turn off symmetry is to add the keyword "noautosym" to
the geometry line.  For example

geometry noautosym
   O 0  0     0
   H 0  1.430 1.107
   H 0 -1.430 1.107
end 

Regards,

Erich R. Vorpagel, Ph.D.     Chief Scientist
Manager Computational Grand-Challenge and Pilot Projects
MSCF Visualization and User Services Group 
Environmental Molecular Sciences Laboratory
Pacific Northwest National Laboratory  
P. O. Box 999,  MS: K8-91
3335 Q Ave.                                  Phone:  509-376-0751
Richland, WA  99352                     FAX:      509-376-0420
Email: erich.vorpagel@pnl.gov 
Web:  http://mscf.emsl.pnl.gov/



-----Original Message-----
From: owner-nwchem-users@emsl.pnl.gov
[mailto:owner-nwchem-users@emsl.pnl.gov] On Behalf Of Van Dam, HJJ
(Huub)
Sent: Monday, February 19, 2007 7:32 AM
To: simon; nwchem-users@emsl.pnl.gov
Subject: RE: [NWCHEM] turn off symmetry

Hi Simon,

To turn the symmetry off in your calculation use the symmetry keyword in
the geometry block but specify the point group C1. For example the
geometry below could be used to do a calculation on the water molecule
without symmetry.

Geometry
   symmetry c1
   O 0  0     0
   H 0  1.430 1.107
   H 0 -1.430 1.107
end 

I have no idea whether turning symmetry off will solve your problem
though. Of course if the denegeneracy persists your MP2 result is
undefined. Is it really necessary to do MP2 at that geometry?

Best wishes,

   Huub

==========================================================
Huub van Dam (h.j.j.vandam@dl.ac.uk, +44-1925-603933)
==========================================================


-----Original Message-----
From: owner-nwchem-developers@emsl.pnl.gov
[mailto:owner-nwchem-developers@emsl.pnl.gov] On Behalf Of simon
Sent: 19 February 2007 14:27
To: nwchem-users@emsl.pnl.gov
Subject: [NWCHEM] turn off symmetry

Hello,

I have a poor convergence problem in a MP2 calculation due a degeneracy
between my HOMO and my LUMO. Here is the error message.

  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  Warning - the HOMO and LUMO are degenerate and you are using symmetry.
  This can lead to non-variational energies and poor convergence.
  Modify the initial guess, or use an open-shell wavefunction, or turn
  off symmetry.
  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

My input coordinates were optimized with DFT and I tried also HF
optimized coordinates but I still got this problem.
My system is not supposed to be open-shell so I didn't not try it.
Finally I didn't find a way to turn off symmetry in the manual.
Does somebody have a clue what I could try?
Is it possible to turn off symmetry in a MP2 calculation?

Thanks in advance,

Simon Pierrefixe
Vrij Universiteit.