## 1F: The z-matrix in the Gamess input file

The conventions used for the Gamess type of z-matrix are
different from the MOPAC format.

MOPAC can generate such a z-matrix. The keyword AIGOUT produces a
Gaussian type of input file, for which the z-matrix part is the
same as for Gamess. The keywords and other directives have to be
replaced.
The main differences are:

alpha-numeric symbols are used for variables,

the reference atoms appear in front of the symbols,

numeric values are interpreted as constants,

the z-matrix is followed by, optionally, a list of variables declared as
constants, and a list of values for the variables in an optimisation.

An example:

TITLE
title line entered here
ZMAT ANGS indicates start z-matrix
C1 origin
C2 1 ccd ccd = distance C2-C1
C3 2 ccs 1 a1 ccs=distance C3-C2, a1=angle C3-C2-C1
H1 1 ch 2 a1 3 0.0 torsion H1-C1-C2-C3 is 0.0
H2 1 ch 2 a1 3 180.0 Even with the directive RUNTYPE OPTIMISE
H3 2 ch 1 a1 4 180.0 these four torsions are kept constant
H4 3 ch 2 a2 1 180.0
H5 3 ch 2 a2 1 d1
H6 3 ch 2 a2 1 -d1 Note symmetry relation with previous torsion
[constants
follows list of constants, if any]
variables
ccd=1.34 list of variables
ccs=1.52
ch=1.09
a1=120.0
a2=109.5
d1=60.0
END marks end of z-matrix
BASIS STO3G specifies basis set
RUNTYPE OPTIMISE type of calculation
VECTORS ATOMS starting guess MO's
ENTER 1 closes input file

Note how symmetry relations are entered by using symbols more than once.
What is the structure of this molecule?

Are all symmetry relations valid?

Other valid basis sets are;

SV 3-21G, SV 4-31G, 6-31G*, TZVP, etc. See the
Gamess manual for an overview.

Alternative RUNTYPE's are:

- SCF single point integrals and SCF calculation
- SADDLE search for saddle point; see chapter 2.
- FORCE force constant calculation at equilibrium geometry

This concludes Chapter 1.

Back to Contents of Chapter 1.

Next chapter How to locate a Transition State.

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