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Hi all,

When I read the output (OUTCAR, e.g.) of the MD calculations (IBRION=0), I am not sure about the definition of the free energy right here. It says :
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FREE ENERGIE OF THE ION-ELECTRON SYSTEM
free energy TOTEN = ***** eV
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But does it only include the electron free energy or all free energies like anharmonic phonon-phonon interactions? I guess the total energy VASP will calculate include everything, but how about entropy, because F=U-TS
Not quite sure about this. Is there anyone familiar with this issue?

Thanks,
Emerald

the free energy in MD runs includes the internal energy U, the electronic contribution to S (temperature-related -broadening), ETOTAL includes the kinetic energy in addition. Phonon contributions are NOT included, as they are not calculated in an MD run (please have a look at the settings of IBRION to calculate vibrations/phonons in particular).

Hi!

Thanks for the clarification here. Not sure if I've missed it, but I think it might be worth mentioning in one of the MLFF wiki pages that the regressed energy (stored in ML_AB) includes the electronic entropy term. At least I originally thought it was the potential energy (e.g. "energy(sigma->0) =") and only realised it was the free energy ("free energy TOTEN") when observing a systematic energy error in the MLFF validation and inspecting the ML_ABN and OUTCAR files.