I am using gaussian09.
I want to calculate triple derivative at the minimum of potential energy surface of acetone to get the cubic anharmonicity constant. For that I need to do energy calculations along the neighborhood of minimum of PES. For that I need to displace the molecule along carbonyl sretching mode of acetone. So my question is how to displace it along one paricular normal mode.
Thanks in advance.
You may be interested in using our python program, pyQRC: https://github.com/bobbypaton/pyQRC
If you have a G09/G16 output file that you want to displace along a particular normal mode (e.g. mode number 17) and generate a new input file you would do the following:
python -m pyqrc output.log --freqnum 17 --amp 0.1 --route 'B3LYP/6-31G(d)' --nproc 4 --mem 8GB --name 01
This creates the file output_01.com, which is displaced along the coordinate of interest. To move in the opposite direction chose a negative amplitude (--amp)
You can open the molecule in Gaussview, Go to Results> vibrations. Select the desired normal mode. At the bottom there is a checkbox called 'manual displacement'. Tick it. Then move the slider to displace the molecule along the selected normal mode. After that you can click 'save structure' to save the displaced structure as a new input file. Not sure if this is what you want. Let me know.
Hi Rugwed - you can follow the approach that Turbasu suggested if you want structures that don't have pre-optimized geometries on the PES. If you want optimized geometries with a certain coordinate frozen doing relaxed PES scans (i.e. the CO stretching mode), you can freeze coordinates with the modredundant option (for your example, freeze the C=O bond and then expand/contract it by little distances). It is worth to mention that this later method might be useful for stretching modes where you can expand/contract a bond, but not much useful for other types of vibrational modes.
You can check this page for more information --> https://gaussian.com/opt/ (the modredundant keyword is in the "Options" tab)
Hope this helps, not sure which option is what you wanted
Turbasu Sengupta In the results section the vibration option is inactive and I am unable to click it. Can you help me regarding this?
Thanks in advance.
For that you need to complete a frequency calculation of your optimized structure (Keyword: Freq https://gaussian.com/freq/). Frequency calculation can be performed as aseparate job after the optimization is finished or you can submit both Opt+freq as a single linked job. In this case Gaussian will automatically start optimization calculation after optimization is finished. Once your output will contain freq data, that option will be active in Gaussview.
You may be interested in using our python program, pyQRC: https://github.com/bobbypaton/pyQRC
If you have a G09/G16 output file that you want to displace along a particular normal mode (e.g. mode number 17) and generate a new input file you would do the following:
python -m pyqrc output.log --freqnum 17 --amp 0.1 --route 'B3LYP/6-31G(d)' --nproc 4 --mem 8GB --name 01
This creates the file output_01.com, which is displaced along the coordinate of interest. To move in the opposite direction chose a negative amplitude (--amp)
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