CCL:G: Fixing distance between point charge and atoms

 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
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