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patonlab / GoodVibes

Calculate quasi-harmonic free energies from Gaussian output files with temperature and other corrections
http://www.patonlab.colostate.edu
MIT License
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Ssym gives different G with C1 #34

Closed dking072 closed 4 years ago

dking072 commented 4 years ago

Hello,

I am using GoodVibes to calculate the quasiharmonic Gibbs free energy of some rather large molecules that are definitely C1. I have experimented with the use of the --ssym option, because there are smaller molecules in the project that do have symmetry. However, when I use the --ssym option on my C1 molecules I appear to get different results. For example, on one particular complex I have:

python -m goodvibes --qs truhlar -t 373.15 -v 0.976 --imag *.out Corrected G: -4939.567977

python -m goodvibes --qs truhlar -t 373.15 -v 0.976 --ssym --imag *.out Corrected G: -4939.565380

The program appears to properly identify the molecules as C1, so I don't think I should be getting a difference between the two values, unless I am mistaken.

Thank you for your excellent program.

luchini18 commented 4 years ago

Hi, Thanks for the submission, this difference you are seeing is coming from the internal symmetry term of the molecule. This term is often used in terms for treating free rotor entropies and since we are employing either Truhlar or Grimme-type corrections to take care of these low-frequency modes, the effect of this internal symmetry term has been effectively eliminated in the most recent update, so you should see no symmetry correction for C1 molecules.