Subject: Summary:Gaussian: Error on Z-matrix card number

From: "William Wei" <william.wei/at/utoronto.ca>
Date: Thu, 4 Dec 2003 14:48:47 -0500

About ten days ago, I posted a question about dealing with the Error on
Z-matrix Card number. I got a lot of valuable replies. Thanks for all the
helps.

Original Q:
If I run relaxed Potential Energy Surface (PES) scan under Gaussian 98, the
Z-Matrix card error always comes to me.
......
 Error on Z-matrix card number   11
 angle Alpha is outside the valid range of 0 to 180.
 Conversion from Z-matrix to cartesian coordinates failed:
......

I explored on this issue. There are two possible situations related to this.
One is the Z-Matrix definition on ring system. The other is the torsional
angle reaching 0 degree. (Please let me know if I am wrong.)

Replies:
This happens to me all the time. Check the angle on atom 11. It's probably
either greater than 180 degrees, or negative. If that's not it, check the
torsion for that atom. It doesn't matter if the torsion is big or
negative, but it the middle angle of the torsion is out of bounds, it will
cause an error (so if it's defined A-B-C-D, both A-B-C and B-C-D have to
be between 0 and 180 degrees, but A-B-C-D can be anything.

Joslyn Kravitz

Generally this problem is solved by adding a dummy atom.
Example
if I have a triatomic molecule ABC and I want to see how the
energy changes as I change the angle ABC from 90 degree's
through 180 degree's inclusive every thing works fine until the angle
hits 180 degree's. Then the program crashes with the error
message you describe. The solution is to make up a new molecule
   X
ABC
where the angle ABX=90 degree's and X is bonded to B. if you then
scan a new angle XBC from 0 to 90 degree's then no problem will
be encountered.  For more complicated situations you'l have to be
a little more inventive, but in general the principle is the same.
Hope this helps,
All the best
Laurence Cuffe

Funny, I have just been wrestling with the same problem myself! I
suspect the second option you mentioned, namely: The Z-matrix only
accepts angles between 0 and 180 degrees, so of course one first has to
make sure there are no 0 or 180 angles in the initial molecule
specification. However, this is sometimes not enough, since it can
happen that an initial structure with an angle close to the cutoff
values gets optimized to a structure where the angle does indeed
"overstep the bounds", causing Gaussian to crash! The solution would be
to redefine the problem atoms in terms of less "dangerous" angles (i.e.
angles which could potentially become less than 0 or more than 180 in
the course of the optimization), using dummy atoms if neccessary, or
simply adding a ModRedundant section and doing the PES scan in redundant
internal coordinates.

Good luck!
Heidi

In my experience, g98 only allows Z-matrix angles to be between 0 and 180
degees.  Some other programs, e.g., mopac, permit them to be between 0 and
360 degrees.

The solution is to redefine your z-matrix.  If you are using WebMO Pro,
there is a z-matrix editor that does exactly that!

Will Polik
------------------

I hope this can help to build our problem-soving database.

William