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I am calculating the zero-point energy (ZPE) from vibrational frequency calculations in VASP, but my computed ZPE is smaller than the reference value for H in the gas phase (0.27 eV). When I subtract my value from half of the ZPE of H₂, I get a negative ZPE, which seems incorrect. I used IBRION = 5, NFREE = 2, POTIM = 0.015 with PAW-PBE potentials. Could this be due to an issue with my settings, or is there a standard correction to ensure accurate ZPE estimation? Any guidance would be appreciated.

Hello,

Thanks for reaching out. I would like to look at your calculation to see what's going on. Could I ask you to provide all the relevant input and output files in the form of a minimal reproducible example?

The calculated value of ZPE is 0.04.
Then, ΔZPE = 0.04 - (0.27 / 2), which results in a negative value.

Is it okay to proceed with this value for Gibbs free energy calculations, or is there an issue with my calculation?

I understand your concern, but that alone is too little information for me to say anything with confidence. That is why I requested the input and output files in my previous answer. Please upload as a zip/tar archive the following files

• INCAR

• POSCAR

• KPOINTS

• OUTCAR

Otherwise, I will not be able to help you with your request.