# Re: CCL:freezing atoms in g03 optimizations

• From: Nicolas Ferré <nicolas.ferre:at:up.univ-mrs.fr>
• Organization: LCTMM
• Subject: Re: CCL:freezing atoms in g03 optimizations
• Date: Wed, 02 Jun 2004 17:37:03 +0200

``` Hi,
```
The fastest way is to use the cartesian coordinates of your system instead of the redundant internal ones. Then in order to optimize only a subset of atoms, use the following notation:
``` Atom_i    0   X_i  Y_i  Z_i
Atom_j   -1   X_j  Y_j  Z_j
```
That means that you freeze the position of atom j while atom i is free to move. Then running a standard optimization job in REDUNDANT INTERNAL COORDINATES is still possible: OPT is enough if the number of atoms is less than 50, or use OPT=REDUNDANT. The internal coordinate builder will add coordinates between active atoms, between active and frozen atoms but not between frozen atoms.
``` Hope this helps,
Nicolas
Alessandro Contini a icrit :
```
``` Hi Joey,
```
yes, the modredundant optimization is a good choice. If you have gaussview the procedure is pretty symple trhough the reduntant coordinate editor. If you are not using gaussview it could be pretty challanging if your sistem is rather big. However you have to put your redundant specifications after a blank line at the end of the g03 input. If you need to freeze an atom coordinate (cartesian) you'll write
``` X N0 F
where N0 is the atom number you want to freeze
if you want to freeze a bond lenght the syntax will be
B N1 N2 F
for an angle
A N1 N2 N3 F
and for a dihedral
D N1 N2 N3 N4 F
where Nn are the respective atom numbers
Hope this help
```
Alessandro Alle 20:51, martedl 1 giugno 2004, Joey Harriman ha scritto:
` `
``` 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.
``` Thanks in advance,
Joe Harriman
----------------------------------
Joe Harriman
Computational Chemistry
University of New Brunswick
Room 228
Toole Hall
s808o:at:unb.ca
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