From owner-chemistry@ccl.net Wed Jan 30 04:30:00 2013
From: "Mariusz Radon mariusz.radon . gmail.com" <owner-chemistry**server.ccl.net>
To: CCL
Subject: CCL: Forces between atoms in molecule
Message-Id: <-48155-130130042901-3172-50i9TPnimS6dO33TYRjcxg**server.ccl.net>
X-Original-From: Mariusz Radon <mariusz.radon*|*gmail.com>
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Date: Wed, 30 Jan 2013 10:28:43 +0100
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Sent to CCL by: Mariusz Radon [mariusz.radon[]gmail.com]
On 30.01.2013 05:19, alireza zeinalinezhad ar.zeinali ~~ yahoo.com wrote:
> Sent to CCL by: "alireza  zeinalinezhad" [ar.zeinali||yahoo.com]
> Dear ccl-netters,
> Does anyone know how to find/print the forces between atoms in molecule/cluster using g09.
> thank you
> Alireza

Hi Alireza:

In order to obtain forces acting on the atoms you can use a small trick:
just do a single step of geometry optimization, i.e., Opt(MaxCycles=1).
The forces would be zero, of course, in the equilibrium geometry.

However, to calculate forces acting on atoms is not really the same as
to calculate "forces between atoms in a molecule/cluster." If I
understood you correctly, I am afraid that what you want to obtain
cannot be uniquely defined because the total energy in quantum chemistry
is _not_ a pairwise inter-atomic potential. Thus, I believe it is not
straightforward to decompose the resulting forces into a sum of
contributions, one from each pair of atoms.

Regards,
Mariusz Radon> 
> 


-- 
Dr Mariusz Radon, Ph.D.
Coordination Chemistry Group
Faculty of Chemistry
Jagiellonian University
ul. Ingardena 3, 30-060 Krakow, Poland
http://www.chemia.uj.edu.pl/~mradon