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50 2 'formatted checkpoint file' - here you put in the name of the .fch file that you generated earlier (you don't need to put in the .fch extension). 3 'Cube file' - The name of the output file, make sure that here you DO add the .cub extension. 4 'Approx points per side' - accept the default. 5 'header' - accept the default. You will find that a .cub file has been created in the G98W directory. Now you can open Orbital Viewer, click on 'open' and browse to the .cub file generated. It will open in the Viewer and you can move it around to look at the molecular orbital from various angles. Other Useful Things 1.If an optimization has already been done use opt=calcfc to get fc for freq. job. 2.Gaussian 98 prints the atomic coordinates in input (Z-matrix) orientation by default only if the number of atoms is less or equal 20. To force G98 to print the coordinates in all cases, use the IOP(99/14=1). It should print the final z-matrix at the end of the output. 3.If you have a structure which has, (for instance), Oh symmetry but G98 can't get this Oh symmetry when doing geometry optimization then you can use a loose tolerance to determine the symmetry. Add IOP(2/17=N), the default for N is 7, you can try numbers smaller than 7 until the program says "Aha.., this is Oh symmetry". 4.For many transition metals e.g. Hg you will need to use a basis set modified with an electrostatic core potential (ECP) which, basically, removes the core electrons from the atom and replaces them with an empirical potential. G98 comes with the LANL2DZ basis and ECP built-in. If you want to use this basis set then set your input to look like the following: #P RHF/GEN Pseudo=read comments... charge multiplicity molecular specifications C N 0 6-31+G(d') **** Hg 0 LANL2DZ **** Hg 0 LANL2DZ The important parts are the Gen and Pseudo=read - this tells Gaussian to look at the end of the input file for the basis set (which can be different for each atom) and the ECP. In the example above we've used carbon and nitrogen, you would put the element symbol for whatever atoms are in your molecule the |
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