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Date: Tue, 30 Nov 2004 18:46:14 -0500
From: "Harrison, Robert J." <harrisonrj@ornl.gov>
Subject: RE: Geometry Optimization with constrains on clusters
To: Felipe Jornada <fjornada@terra.com.br>, nwchem-users@emsl.pnl.gov
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You can specify the geometry in cartesian coordinates
and then constrain the distance between the ion and
one (or more) of the carbon atoms.  Not quite as
easy as specifying relative to the barycenter, but
ultimately equivalent.

Something like this

geometry
  <put your cartesian coords here as usual>
  zcoord
    bond 1 2  2.2  # use appropriate atom numbers and distance
  end
end

Robert

 


Robert J. Harrison - (865) 241-3937 

-----Original Message-----
From: owner-nwchem-developers@emsl.pnl.gov
[mailto:owner-nwchem-developers@emsl.pnl.gov] On Behalf Of Felipe
Jornada
Sent: Tuesday, November 30, 2004 4:28 PM
To: nwchem-users@emsl.pnl.gov
Subject: Geometry Optimization with constrains on clusters


Dear nwchem users,

I am dealing with the following problem: I have an ion near a fullerene 
molecule, and I want to optimize the fullerene geometry by fixing the
ion 
position. However, I need to have the ion-fullerene distance fixed (i.e.
fix 
the barycenter, otherwise all that happens is the cluster to move away.

Is it possible to avoid this on nwchem? I have read the user's manual,
but I 
found is that I can only fix an atom completely, and not only one of its

coordinate (which would solve this problem). Another solution may be to
use 
ZMatrx, but describing this system would be a rather difficult task.
Right 
now I am developing a "driver" for optimizing this geometry, by
following the 
gradients and correcting the barycenter, but I rather find an easier 
solution, if there is such a thing.

Thanks,

Felipe Jornada