This is by far the best video on Gaussian. Thank you So much For this video. I am going to share it with all my co-teachers and students. Thank you once again for this video.
Thanks for the great lecture. under the frequency calculation output, how do we assign symmetry of the vibrational motion? I could only see only three As in the example you provided, how do we know if it is A1g, A2g and the likes?
You cannot assign the symmetry after the geometry optimization. The time to impose symmetry restrictions is at the building step. If you are using GaussView, look at the help files about the "symmetrize" function. Here's a short description: flex.phys.tohoku.ac.jp/texi/gview/symmetry.htm You can google more resources related to this.
@@dw-pchem Thank you so much for the response. If Imposing symmetry before geometry optimization before frequency calculation, does this in anyway affect the optimization process? for example maybe we might end up having some imaginary frequencies after the frequency calculation
@@afeezadegoke1326 yes. You are right. Imposing symmetry can lead to imaginary frequencies. Then you animate the imaginary frequencies in GaussView / Results / Vibrations... . Then change the geometry along the path of the imaginary frequency. Use keyword nosymm. And reoptimize with opt freq
When I performed the optimization of the minimum four convergence criteria are met and then I carried out a calculation of frequencies which were all real, but to review the criteria for convergence of frequencies two criteria not met: Item Value Threshold Converged? Maximum Force 0.000022 0.000450 YES RMS Force 0.000006 0.000300 YES Maximum Displacement 0.014118 0.001800 NO RMS Displacement 0.002399 0.001200 NO in addition, the output file 09 does not set a gaussian error during calculation. What do I have to do to fix the convergence criteria of the frequencies?
Physical Chemistry (PCHEM) at Sam • 13 minutes ago This suggests your molecule has some very low frequency vib modes. If they are not imag in the freq calc, then you are fine. The max displacement and rms displacement are large because of the flat potential energy surface around the low freq vib mode. I wouldn't worry about it if the freq calc showed all real freqs. That's my answer.
My frequency calculations had been resulting in imaginary frequencies. Is there a simple way to fix it? I’ve tried opt=verytight and also using pyqrc to change the coordinates but they don’t seem to help.
Probably you've solved but try to change the initial geometry, maybe start to optimize at low level of theory with small basis set (i.e HF/3-21G), and gradually reach your level.
This is by far the best video on Gaussian. Thank you So much For this video. I am going to share it with all my co-teachers and students. Thank you once again for this video.
Thank you for the encouragement!!
I have been searching for this information since a long time.. your channel proved to be a blessing for me and for other students in Pakistan
So happy to play a role in your education in Pakistan. What a miracle in this modern age!
Thank u very much lots of love from india
Thank you very much Sir
Hi Dr William, can I calculate optical activity using Gaussian software? Thank you
I never have done that so i am not sure. You can go to Gaussian.com and search in their help files. their files are quite thorough.
Thanks for the great lecture.
under the frequency calculation output, how do we assign symmetry of the vibrational motion? I could only see only three As in the example you provided, how do we know if it is A1g, A2g and the likes?
You cannot assign the symmetry after the geometry optimization. The time to impose symmetry restrictions is at the building step. If you are using GaussView, look at the help files about the "symmetrize" function. Here's a short description: flex.phys.tohoku.ac.jp/texi/gview/symmetry.htm
You can google more resources related to this.
@@dw-pchem Thank you so much for the response. If Imposing symmetry before geometry optimization before frequency calculation, does this in anyway affect the optimization process? for example maybe we might end up having some imaginary frequencies after the frequency calculation
@@afeezadegoke1326 yes. You are right. Imposing symmetry can lead to imaginary frequencies. Then you animate the imaginary frequencies in GaussView / Results / Vibrations... . Then change the geometry along the path of the imaginary frequency. Use keyword nosymm. And reoptimize with opt freq
@@darren.williams Thank you so much prof. I really appreciate your prompt response
When I performed the optimization of the minimum four convergence criteria are met and then I carried out a calculation of frequencies which were all real, but to review the criteria for convergence of frequencies two criteria not met:
Item Value Threshold Converged?
Maximum Force 0.000022 0.000450 YES
RMS Force 0.000006 0.000300 YES
Maximum Displacement 0.014118 0.001800 NO
RMS Displacement 0.002399 0.001200 NO
in addition, the output file 09 does not set a gaussian error during calculation.
What do I have to do to fix the convergence criteria of the frequencies?
Physical Chemistry (PCHEM) at Sam
• 13 minutes ago
This suggests your molecule has some very low frequency vib modes. If they are not imag in the freq calc, then you are fine. The max displacement and rms displacement are large because of the flat potential energy surface around the low freq vib mode. I wouldn't worry about it if the freq calc showed all real freqs. That's my answer.
Sir can you please make a vedio on ONIOM model explaining the input and output files
I'd like to but I have never performed an ONIOM calculation. Let me know if you find a good video on this.
My frequency calculations had been resulting in imaginary frequencies. Is there a simple way to fix it? I’ve tried opt=verytight and also using pyqrc to change the coordinates but they don’t seem to help.
Probably you've solved but try to change the initial geometry, maybe start to optimize at low level of theory with small basis set (i.e HF/3-21G), and gradually reach your level.