(Gaussian,GAMESS)
Next, open a log file containing the results of a freq calculation. It isn't necessary to specify whether you wish to calculate the IR or the Raman spectrum - the IR spectrum will always be calculated, and the Raman spectrum will be calculated if you ran a freq=raman job.
Choose Frequencies from the list of operations on the left.
Parameters for Frequencies
The spectra will be calculated for wavelengths between Start and End. The units of Start and End are cm-1.
This parameter determines the number of points in the calculated spectra.
The Full Width at Half Maximum of each peak.
You can choose either a general or individual scaling factor (see below).The calculated frequencies are multiplied by the scaling factor. The scaled frequencies are then used to generate the spectra.
Click on the GaussSum icon to run the script.
The spectra are convoluted with Lorentzian curves and then plotted with Gnuplot.
Information on the each spectrum and on the normal modes are written to gausssum2.1/IRSpectrum.txt and gausssum2.1/RamanSpectrum.txt.
The first few lines of an example RamanSpectrum.txt are shown below. Tabs are used to separate each column of information. This allows easy import into spreadsheet software (e.g. Excel), just by right-clicking on the file and choosing "Open with".
Spectrum Normal Modes Freq Raman act Mode Label Freq Raman act Scaling Unscaled freq 8 1.6546102666 1 E 35.3144 15.9332 1.0 35.3144 16 3.08064395926 2 E 35.3161 15.9269 1.0 35.3161 24 7.72718233926 3 A1 35.8277 14.6672 1.0 35.8277 32 32.0223114314 4 E 41.3651 1.1718 1.0 41.3651 40 27.9242662176 5 E 41.367 1.1737 1.0 41.367
If you want to use individual scaling factors, you should open a previously created IRSpectrum.txt or RamanSpectrum.txt and edit the column titled 'Scaling Factors'. You can do this in (for example) Excel, and then save as 'Tab Delimited'. Run the Frequencies option again but choose individual scaling factors this time. The new IRSpectrum.txt or RamanSpectrum.txt will contain the scaled frequencies.