Chemical Forums

Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: tulip11 on February 24, 2018, 10:51:35 AM

Title: Gauss09 anharmonic frequencies calculations
Post by: tulip11 on February 24, 2018, 10:51:35 AM

Not sure if this is the right place for this question but I'm currently doing a piece of homework using gauss09 to caluclate anharmonic frequencys. I'm looking at the difference in harmonic/anharmonic frequencies for the group 15 XH3 group.

When I try to calcualte the frequencies for AsH3, the output file show approximetly correct frequencies for the harmonic frequencys but all the anharmonic frequencies come back negative! I am not very experienced using gauss09 so I am unsure why this is or if there is a problem with my input file. As far as i can see the geometry optimisation is correct and the calcualtion worked with NH3 and PH3. I am usingκ B3LYP functional and 6-31G basis set. Any suggestions on how to obtain correct frequencies would be very much appreciated (I have attached pictures of the input/output file for reference)

Title: Re: Gauss09 anharmonic frequencies calculations
Post by: Corribus on February 27, 2018, 09:53:53 AM

Hi Tulip,
Unfortunately from recent past experience, we don't have any regulars here who know a lot about Gaussian calculations. I did a lot of them back in early grad school, but that's too long ago for me to be any help. Doesn't Gaussian maintain a technical support line? I seem to recall asking them many questions back in the day and they were very helpful.

http://gaussian.com/help/