From owner-chemistry*- at -*ccl.net Wed Jun 20 05:40:00 2007
From: "=?ISO-8859-1?Q?=D6d=F6n?= Farkas farkas() chem.elte.hu" <owner-chemistry###server.ccl.net>
To: CCL
Subject: CCL:G: Fixing distance between point charge and atoms
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Date: Wed, 20 Jun 2007 11:12:20 +0200
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Sent to CCL by: =?ISO-8859-1?Q?=D6d=F6n?= Farkas [farkas^^chem.elte.hu]
Hi Chunyi

You can try using a pure Z-matrix (it also allows the use of Cartesains)
or use redundant internals with some atoms (3 or more) frozen in the
Cartesian space. Unfortunately, ghost atoms are not allowed in the
definition of redundant internals. Check the manual for the possible
options.

Good luck,

Ödön

On Wed, 2007-06-20 at 00:39 -0400, Chunyi Sung juneyi1*|*yahoo.com.tw
wrote:
> Sent to CCL by: "Chunyi  Sung" [juneyi1(~)yahoo.com.tw]
> Hi, CCLers
>  
>       I am trying to optimize some molecules in the presence of point charges using the keyword "charge" in Gaussian; however, in my case, some O atom in the molecule always ended up colliding with a positive point charge during geometry optimization. Therefore, I want to somehow set up some constraints on that O atom so that it will stay, say, 2.7 Angstrom away
> > from the positive point charge, does anyone know how to do that ?
> 
>       Originally, I wanted to put a ghost atom right at the location of the positive point charge, and then use "modredundant" to fix the bond length between the O atom and the ghost atom. However, with the "charge" keyword to include point charges, "Opt" must have "Z-matrix", which does not work with "modredundant". So I am now running out of ideas. I'll appreaciate if
> anybody has any suggestions on this. 
> 
> thanks
> 
> chunyi> 
> 
> 
-- 
Ödön Farkas
Associate professor
Deparment of Organic Chemistry and
Laboratory of Chemical Informatics,
Institute of Chemistry,
Eötvös Loránd University, Budapest
Address: 1/A Pázmány Péter sétány,
H-1117 Budapest, Hungary
Phone: +36-1-372-2570
Cell phone: +36-30-255-3111
Fax: +36-1-372-2620
URL: http://organ.elte.hu/farkas