Gaussian frequency job after optimization

In summary, it is possible to directly feed in old Gaussian output or checkpoint files into a new frequency job. This can be done by using the "freq" keyword to indicate a frequency calculation, the "geom=checkpoint" keyword to use the optimized geometry from the previous calculation, and the "guess=read" keyword to read in the wavefunction from the previous calculation. This will save time and resources since Gaussian will not have to recompute the optimized geometry or wavefunction.
  • #1
angura
11
0
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
 
Last edited:
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  • #2
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!
Scientist at [Your Institution]
 

Related to Gaussian frequency job after optimization

1. What is a Gaussian frequency job after optimization?

A Gaussian frequency job after optimization is a computational method used in computational chemistry to determine the molecular vibrational frequencies and corresponding energy levels of a molecule. This is done by optimizing the molecular structure and then calculating the second derivative of the energy with respect to the nuclear coordinates.

2. How is a Gaussian frequency job after optimization performed?

A Gaussian frequency job after optimization is performed using specialized software, such as Gaussian or ORCA, that utilizes quantum mechanical calculations to determine the molecular vibrational frequencies. The software uses an iterative process to optimize the molecular structure and calculate the second derivatives of the energy, resulting in the final vibrational frequencies.

3. What are the applications of a Gaussian frequency job after optimization?

Gaussian frequency job after optimization is used in various fields of chemistry, such as drug discovery, material science, and environmental studies. It is also used in theoretical chemistry to validate theoretical models and understand the properties of molecules.

4. How accurate are the results from a Gaussian frequency job after optimization?

The accuracy of the results from a Gaussian frequency job after optimization depends on several factors, such as the level of theory used, the size and complexity of the molecule, and the computational resources available. Generally, the results are considered to be highly accurate and reliable for most applications.

5. Are there any limitations or challenges associated with Gaussian frequency job after optimization?

One of the main limitations of Gaussian frequency job after optimization is the computational resources required. As the size and complexity of the molecule increases, the computational cost also increases, making it challenging to study larger systems. Additionally, the accuracy of the results can be affected by the choice of the level of theory and the approximations made in the calculations.

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