hi,
I use ZPE=1/2 sum(hVi) to calculate the ZPE energy. There are always some small imaginary frequency for stable geometries. Should I include the imaginry frequency in the ZPE equation? Thanks for suggestions!
ZPE correction
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Re: ZPE correction
No, you need to accurately calculate your frequencies. You can look for posts about this (there are quite a few). Make sure to have a well-converged stationary point, and then use a small ediff=1e-8 and test for convergence using displacements in the range of 0.01-0.001 Ang.
Re: ZPE correction
Thanks!
In the INCAR of optimization, I set EDIFF=1e-4, EDIFFG=-0.02 and it is well converged.
Then I use EDIFF=1e-8, POTIM=0.002 to calculate the frequency,but it still has two small imaginary frequency (43 and 44 cm-1).
What should I do to get all positive frequency? Pls give some suggestions! Thanks!
In the INCAR of optimization, I set EDIFF=1e-4, EDIFFG=-0.02 and it is well converged.
Then I use EDIFF=1e-8, POTIM=0.002 to calculate the frequency,but it still has two small imaginary frequency (43 and 44 cm-1).
What should I do to get all positive frequency? Pls give some suggestions! Thanks!
Re: ZPE correction
If your system has no frozen atoms, you will have zero modes associated with translation and/or rotation. These, you can not include in a harmonic approximation of ZPE.
But if you have frozen atoms, there should be no zero or negative modes. In this case, try going to a lower ediffg, and make sure that your modes are converged with respect to the finite difference displacement.
But if you have frozen atoms, there should be no zero or negative modes. In this case, try going to a lower ediffg, and make sure that your modes are converged with respect to the finite difference displacement.