How to find the % contribution of a group to each molecular orbital (PDOS)

In order to define the atoms which comprise a group, a file, gausssum1.0/groups.txt, should be created with a format similar to the following:

Ru
1
bpy1
2-11,14,17,22,27,34-35,42-43,50,57
bpy2
12,16,18-19,25-26,28-30,39-41,44-46,54-56,58,61
bpy3
13,15,20-21,23-24,31-33,36-38,47-49,51-53,59-60
			

The example above is of [Ru(bpy)3]2+, an inorganic complex. It describes how different atoms belong to different groups that we are interested in. The numbers were obtained by opening the output file in GaussView and turning on the labels. groups.txt needs to obey the following rules:

A single point calculation should be done with the following keywords: (Gaussian) pop=full iop(3/33=1,3/36=-1), (GAMESS) NPRINT=3. This creates a large log file containing information on the overlap matrix among other things. (Note: the 3/36=-1 option for Gaussian prevents the calculation and printing of the multipole matrices; this is purely to keep the output file size as small as possible. In some cases, for example SCRF calculations, the multipole matrices must be calculated - if so, leave out the 3/36=-1. It will not affect the calculation of the PDOS.)

Using GaussSum open the log file and choose MO.py. Pick the DOS option. See the previous section for information on the options.

Click on the GaussSum logo. GaussSum calculates the percent contributions of each of the groups to each of the molecular orbitals. This may take a few minutes.

Afterwards, the partial density of states spectra (PDOS) are plotted. Note that each one is stacked on top of the previous one, which means that the line at the greatest height is equal to the sum of all of the partial density of states, and hence equal to the total density of states spectrum. Information on the spectra is written to gausssum1.0/DOS_spectrum.txt.

Information on the molecular orbitals and the percent contributions of the groups is written to gausssum1.0/orbital_data.txt. The last few columns of orbital_data.txt contain more accurate values for the percent contributions and is used by UVVis.py. You should not edit this file if you wish to use the information in it to calculate the changes in charge density associated with electronic transitions, as described in Chapter 7, How do I get the UV-Vis or circular dichroism spectrum of a molecule?.

Creation of PDOS spectra is also supported for unrestricted calculations with Gaussian. The spectrum plotted is of the total DOS broken down by the contribution of each of the groups. orbital_data.txt contains information on the breakdown of the alpha and beta electrons by group.

If you wish to redraw the PDOS spectrum, perhaps with a different value for FWHM, there is no need to recalculate the % contributions of each of the groups. Simply tick the box for "Use existing orbital_data.txt" and the graph will be created much faster. (Note: this does not work for unrestricted calculations.)