Z-matrix,summary

• From: kozelka : at : citi2.fr (JirKa Kozelka)
• Subject: Z-matrix,summary
• Date: Sat, 30 Nov 1996 19:02:33 +0100 (MET)

``` Dear netters,
Some days ago, I submitted the following question:
************
Just a simple question concerning geometry optimization using G94.
If you want to keep the local symmetry of a functional group, say,
a methyl group, how do you do it? Can one use algebraic expressions
in the Z-matrix, such as in the following input for acetaldehyde:
H
C   1   1.08
O   2   1.33   1   120.
C   2   1.54   3   120.   1    180.
H   4   ch     2   hcc    1    hcch
H   4   ch     2   hcc    1    hcch+120.
H   4   ch     2   hcc    1    hcch-120.
ch  1.01
hcc  120.
hcch  180.
*****************
I have obtained several replies from kind people. The solution is
quite simple, so I am a little ashamed. Nevertheless, it is good
to know that G94 does not accept composite expressions.
As an example, I reproduce below the reply from Stefan.
********************
Hi JirKa,
in G94 you have to use popt (or addredundant), if you want to constrain some
degrees of freedom. It implies opt=z-matrix instead of the normal redefinition
of your structure into redundant internal coordinates.
You must not use algebraic expressions like "hcch+120" in the
z-matrix, but you can achieve the same effect with the following z-matrix:
H
C   1   1.08
O   2   1.33   1   120.
C   2   1.54   3   120.   1    180.
H   4   ch     2   hcc    1    hcch
H   4   ch     2   hcc    5    120.
H   4   ch     2   hcc    5    -120.
ch  1.01
hcc  120.
hcch  180.
Yours,
Stefan
Stefan Fau,               fau : at : mailer.uni-marburg.de
FB Chemie der Philipps-Universitaet Marburg,
Hans-Meerwein-Str.
D-35032 Marburg
***************************
Jirka Kozelka
Universite Rene Descartes, Paris
kozelka : at : citi2.fr
fax +331-42 86 83 87
```