Subject: A REPLY TO GAUSSIAN PROBLEMS (ANGLES ETC) QUERY

From: "E. Lewars" <[email-masked]>
Date: Wed, 31 Aug 1994 17:06:01 -0400

[email-masked]  asked (1) about problems with angles of 180, and
(2) jobs failing with large basis sets and some kind of error message
For problem(2) you may heve to contact Gaussian.
For the 180 problem there are two solutions.  If you are are using Z-matrix
input (which I think Gaussian wants you to; the progaram is oriented 
toward that, and some things won't work with Cartesian input) then the 
standard way to avoid your problem is to use a dummy atom, usually 
denoted X, in the Z-matrix so that a 180 angle never arises.  Put
X 1. (1.0 A) awat from some atom and make angle A-atomx-atomy = 90.
Z-matrices are discussed in detail in Tim Clarke's *A Handbook of
Computational Chemistry*,; see also Hehre et al *Ab Initio Molecular Orbital
Theory* and Foresman and Frisch *Exploring Chemistry with Electronic 
Structure Methods".  If you write your Z-mat. like
C1
C2  C1  C2C1
H3  C1  H3C1  C2  A312
H4  C1  H4C1  C2  A412  H3  D4123
H5  C1  H5C1  C2  A512  H3  D5123
X6  C2  1.    C1  90.   H3  0.
etc, etc, it will be less of a pain to interpret
The other solution is to forget z-matrices and use Cartesians (x,y,z), if
Gaussian will let you (there are some programs that won't even let you
think of a Z-matrix0.
---
Errol Lewars