Gaussian frequency job after optimization

[angura]

Hi,

I already got some good Gaussian-help in this forum, so maybe somebody can help me once again :)
I did an optimization run for my structure in Gaussian and didn't know, that I could have combined this with a frequency calculation. So now I have to start a new frequency job based on my optimized geometry.

My question:
Can I somehow directly feed in the old Gaussian output or checkpoint file into the new job?
Because at the end of the optimization run I have all the informations on the approximated wavefunction for the optimized geometry, so I think it would be very inefficient if Gaussian would have to recompute all of this for a frequency job.
So is there any way, to re-use more than just the optimized positions of the atoms?

Thanks in advance,
angu

 

[Zefram]

yenHi anguyen,

Great to hear that you have found helpful support in this forum before. I would be happy to assist you with your current question.

Yes, it is possible to directly feed in the old Gaussian output or checkpoint file into the new frequency job. This is known as a frequency calculation on a "frozen" geometry. Essentially, you are using the optimized geometry from your previous calculation as a starting point for the frequency calculation.

To do this, you will need to specify the following in your input file:
- Use the "freq" keyword to indicate that you want a frequency calculation.
- Use the "geom=checkpoint" keyword to specify that you want to use the optimized geometry from the previous calculation.
- Use the "guess=read" keyword to read in the wavefunction from the previous calculation.

By using these keywords, Gaussian will not have to recompute the optimized geometry or the wavefunction, which will save you time and resources.

I hope this helps. Good luck with your frequency calculation!
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