Chapter 6. How do I extract molecular orbital information?
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# Chapter 6. How do I extract molecular orbital information?

This chapter has been divided into three sections. The first section describes how to extract information on the eigenvalues and symmetries of the molecular orbitals. The second section describes how to extract information on the contributions of groups of atoms to each of the molecular orbitals. The third section describes how to extract information on the nature of the overlap between different groups of atoms.

## How to extract basic information (DOS)

Open the log file containing the relevant information and choose Orbitals from the list of operations on the left. Pick the DOS option.

The boxes labeled "Start" and "End" are the start and end points (in eV) of the density of states spectrum. The box labeled "FWHM" is the full width at half-maximum (in eV) of the gaussian curves used to convolute the DOS and COOP spectra.

Click on the GaussSum logo to start the script. The molecular orbital information is written to `gausssum3.0/orbital_data.txt`.

The density of states (DOS) spectrum is convoluted using Gaussian curves of unit height and the specified full width at half-maximum. Gnuplot is then used to plot the spectrum. The details are written to `gausssum3.0/DOS_spectrum.txt`.

If you tick the box labelled "Create originorbs.txt?", a file `gausssum3.0/orginorbs.txt` will be created which can be used to plot the orbital energies as a series of bars, one above the other, using a program such as Origin (Windows) or Grace (Linux). See the worked example on the GaussSum web site for more information.

Unrestricted calculations are supported for Gaussian. The same files are created but with the data broken down into sections for alpha and beta electrons. The DOS spectrum plotted is also different, containing an alpha DOS, a beta DOS and a (scaled) total DOS. If you ticked the box to create `originorbs.txt`, the beta eigenvalues are listed after all of the alpha eigenvalues.

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Chapter 5. How do I get the IR or Raman spectrum of a molecule? | Home | How to find the % contribution of a group to each molecular orbital (PDOS)