For calculation Pre-resonance Raman, Gaussian 09 manual says as below:
This calculation type is requested with one of the Raman options in combination with CPHF=RdFreq. The frequency specified for the latter should be chosen as follows:
1. Determine the difference in frequency between the peak of interest in the Raman spectrum and the incident light used in the experiment.
2. Perform a TD calculation using a DFT method in order to determine the predicted location of the same peak.
3. Specify a frequency for CPHF=RdFreq which is shifted from the predicted peak by the same amount as the incident light differs from the observed peak.
I understand the first step. But in the second step, it says "TD-DFT calculation to determine the predicted location of the same peak" what does that mean? I think TD- DFT give UV peaks. Is it talking about UV peaks or something else. Could anyone guide me how to calculate the pre-resonance Raman, say it for Benzene?
Imagine your incident light is at 500nm and your peak of interest at 450nm. Then the difference is 50nm. Let's say your TD calculation predicts the peak of interest at 420nm. Then you should set CPHF=RdFreq with 470nm.
Dear guys,
I am running Pre-resonance Raman calculation at wave length 282nm. It does not convergent. So I try to decrease convergence criteria to 6. It gives me error termination after I submitted a job? I uploaded I/O files. Someone please help me!
Thank you for the help!!!
Hi Rishat,
First try to optimize your structure with the usual tricks and add a normal frequency calculation i.e.
#p opt freq b3lyp/6-31g(d,p) scf=(qc,maxcyc=1000)
Once you have a reasonable structure with no imaginary frequencies then run your Raman calculation with the keywords polar=raman cphf=rdfreq with force constants read-in from the previous checkpoint file. I would not recommend decreasing the convergence criteria in the scf.
Dear Prokopis,
I am really thanks to you. I submitted the calculation let me try then tell you what happen.
Dear Prokopis,
I get a result. I try to see the Raman spectra on the Gaussview. Unfortunately, I did n't see the Raman instead I saw IR.
I send you the log file. Could you help me look at it?
Thank you
Dear Swathi,
The question is how do you extract Raman freq from the *.chk file?
Thanks,
Rishat
Get the path of the software g09 where formchk file is present. Type g09 path/ formchk filename.chk filename.fchk. this will generate readable fchk file which has the data.
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