# CCL:G: Symmetry constraint during scan calculation

*From*: Víctor Luaña Cabal
<victor:+:fluor.quimica.uniovi.es>
*Subject*: CCL:G: Symmetry constraint during scan calculation
*Date*: Wed, 16 Sep 2015 17:44:57 +0200

Sent to CCL by: =?iso-8859-1?Q?V=EDctor_Lua=F1a?= Cabal [victor *
fluor.quimica.uniovi.es]
On Wed, Sep 16, 2015 at 05:01:27PM +0530, Mohan maruthi sena maruthi.sena-
-gmail.com wrote:
> 1) I have given symmetry=follow key word in g09 input file and it has
> followed the initial symmetry. Suppose my initial symmetry is octahedral
> and if I want to scan an angle in d3h symmetry, How can I mention this
> point group in input file. Is there in any option to mention point group in
> g09?
Mohan,
Symmetry is recognized by gaussian g09 from the geometry of your system.
That differs in many other codes (gamess for instance) where the symmetry
can be given beforehand to simplify entering the geometry. If you want
to see is your system in unstable against a D3h deformation you should
try a small D3h deformation before optimizing the geometry. Analyzing
the frequency vibrations will also give you a hint of the instability.
Remember that QM codes use symmetry to reduce the computer time for
obtaing the integrals required to compute energy, gradient and hessian
of the problem.
You can force g09 to avoid symmetry by nosymm. Check input:
<http://www.gaussian.com/g_tech/g_ur/k_symmetry.htm>;
Good luck,
Víctor Luaña
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