# Re: CCL:freezing atoms in g03 optimizations

• From: Yohann Moreau <moreau[at]lctn.uhp-nancy.fr>
• Organization: Equipe de Chimie et Biochimie Théoriques
• Subject: Re: CCL:freezing atoms in g03 optimizations
• Date: Wed, 02 Jun 2004 16:21:28 +0200

Hello Joey,

If I understand, you just want to make a partial geometry optimization, i.e. without moving some atoms of the molecule.
To do so, there are two ways in Gaussian : it depends if you use cartesian coordinates or a z-matrix

In the first case, just put the flag "-1" between the atom type and its coordinates (see my answer to Kadri a few days ago)
(just be careful not to put a non frozen atom in first which is atomatically frozen)

In the second, you'll freeze internal coordinates :
use the keyword "opt=z-mat"
write your Z matrix not with numerical values but with variables

after your Z matrix, you must give values to the variables : name of the variable follewd by the value
(this is in fact the general way to write a Z-matrix, nothing new)
To freeze some values, juste put in first the set of variables, a blank line and second, the set of constants.
I'm not sure to be clear enough, so here is an example :

# RHF/STO-3G opt=z-mat

title : methanol

0 1
C
H   1   R1
H   1   R1   2   A1
H   1   R1   2   A1   3 D1
O   1   R2   2   A1   3 -D1
H   5   R3   1   A2   2 D2

R1 1.083
R2 1.44
A1 109.47122
D1 120.0

R3 0.96
A2 104.48
D2 180.0

R1, R2, A1 and D1 will be allowed to vary whereas R3, A2 and D2 won't be.

Yohann

Joey Harriman wrote:

Hi,

I am trying to do a geometry optimization on a large system which contains some atoms
that are involved in a transition-state structure.  I would like to fix the portion of
the molecule with the TS geometry and do an optimization on the rest of the atoms.
What is the best method to freeze the TS atoms?  I have been looking at the
ModRedundant function, but am unaware of how to create the secondary input after the
zmatrix for this.  Any help would be greatly appreciated.

Joe Harriman

----------------------------------
Joe Harriman
Computational Chemistry
University of New Brunswick
Room 228
Toole Hall
s808o[at]unb.ca
----------------------------------

-= This is automatically added to each message by the mailing script =-
To send e-mail to subscribers of CCL put the string CCL: on your Subject: line
and send your message to:  CHEMISTRY[at]ccl.net

Send your subscription/unsubscription requests to: CHEMISTRY-REQUEST[at]ccl.net

If your mail is bouncing from CCL.NET domain send it to the maintainer:
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

```--

Yohann MOREAU,
Doctorant
Equipe de Chimie et Biochimie
Théoriques

UMR CNRS-UHP 7565 "SRMSC"
BP 239, F-54506
Vandoeuvre-lès-Nancy
http://www.lctn.uhp-nancy.fr/Etudiants/Yohann.Moreau.html```