Preparing Gaussian input file

An input file (.GJF extension)  ready to be submitted to Gaussian98/03 program is prepared by MOLDRAW, by the (File--->Export to...--->Gaussian98) menu.

A form with the most important options is provided. Please consider that the molecule will be saved in cartesian coordinates only (no Z-matrix) and that, at the moment, only a small subset of the available Gaussian03 options can be specified.

If ONIOM layers have been previously specified, the form automatically pops up with the two layers specification. MOLDRAW also compute the actual molecular charge and spin multiplicity (2S+1, where S is the total spin component) so that the user can check for some inconsistencies in the structure.

When molecular mechanics optimizations are requested (either UFF or DREIDING) Gaussian will adopt a different optimization algorithm, which is particularly efficient compared to the one adopted for QM methods. In this case, however, the optimized geometry is no longer printed at the end of the calculation. In order for MOLDRAW to read the final optimized geometry a two steps input file is written: in the first part the optimization is carried out while in the second part the optimum geometry will be read back from the checkpoint file. The geometry displayed by MOLDRAW will then be the optimized one.

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