The Shodor
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Gaussian 94 (abbreviated G94) is a high-powered computational tool. It is most often run on a workstation cluster or a supercomputer because of the computational expense associated with the level of accuracy it produces. Gaussian 94 does several types of calculations, including single-point energy calculation, geometry optimization, transition state location, vibrational frequency calculation, thermochemical analysis, excited states calculation, including solvent effect, and calculaton of electrostatic potential-derived charges and polarizabilities. An extremely wide variety of ab initio and semi-empirical methods are supported.
In this course we will only encounter Gaussian briefly, but the readings here (as well as other resources) can give you a good basic understanding of Gaussian.
Gaussian 94 requires the submission of a text file giving the type of job to be run and the molecule. When the run is completed, Gaussian returns a text file with the output in alphanumeric format. These output files can be quite long and complex. We will learn to interpret the relevant parts of them; visualization tools are available to generate graphical renderings of Gaussian's output.
While the possibility of using a supercomputer may be impressive, the complexity of Gaussian's input and output files may seem daunting at first. A graphical-interface molecule builder seems like a comforting resort at this point; but there are distinct advantages to using G94 which outweigh the initial inconveniences of a textual interface. These include the ability to follow reaction pathways and scan potential energies in one job submission (rather than tedious and repetitive single point energy submissions to a graphical program) as well as the higher level of accuracy, greater choice in the theory used, and far more freedom in molecule construction.
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