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.
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 fileNote 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: