CCL:G: Fixing distance between point charge and atoms

 Sent to CCL by: "Gustavo Seabra" [gustavo.seabra:-:gmail.com]
 You can try adding an additional electron-repulsive term to the point
 charge, as described in the Gaussian webpage:
 http://gaussian.com/g_ur/k_charge.htm
 HTH,
 Gustav Seabra.
 > -----Original Message-----
 > From: owner-chemistry%%ccl.net [mailto:owner-chemistry%%ccl.net]
 > Sent: Wednesday, June 20, 2007 12:39 AM
 > To: Seabra,Gustavo
 > Subject: CCL:G: Fixing distance between point charge and atoms
 >
 >
 > 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