This guide is intended to provide enough information about GAUSSIAN that one can construct an input file and run a basic calculation of energy and molecular properties. Both programs have many more capabilities than are described here, and anyone who intends to make a serious exploration of computational chemistry should read the full documentation for each program.

Since we do not have the separate graphical interface for GAUSSIAN, input files must be constructed "by hand"; that is, the user must use a text editor to create a file containing instructions about what type of computation is to be run, and providing an initial structure on which the program will operate. Alternatively, PCModel will write a respectable Gaussian input; be sure to check it before using it, however.

When constructing a Z-matrix, which provides input that does not need Cartesians, I find it helpful to work with pencil and paper, creating the entire Z-matrix before firing up the editor. Cartesian coordinates for input may be obtained by cutting and pasting from a SPARTAN or PCModel file.