Using Variables in a Z-matrix

Here is a complete input file for an optimization of this molecule  

Note that there are no blank lines within the Z-matrix, despite its appearance here. The extra spacing in this example is simply an artifact of the commentary. 

Exploring Chemistry with Electronic Structure Methods 

This file introduces the concept of variables within the molecule specification. Here, variables are simply named constants variable names are substituted for literal values within the Z-matrix, and their values are defined in a separate section following it. The two sections are separated by a blank line, or a line with a blank in the first column and the label Variables placed elsewhere on it (this is one exception Gaussian makes in its requirement for completely blank lines).  

Notice that we used D and -D respectively for the dihedral angles for the non-planar hydrogens, as opposed to two separate variables. This is done to ensure symmetry within the molecule. 

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