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I am using pyscf Hartree-Fock method to calculate total energy for a conventional unit cell of carbon diamond using one of the example scripts that the developers made. The script outputs the following: HF energy (per unit cell) = -43.846800286076409. I have learned on Matter Modeling that the units are Hartree. That means the HF energy is -1193.1322182 eV. So I guess that means I can divide by the number of atoms in the cell to get the HF energy per atom: -1193.1322182/8 = -149.141527275. So HF energy is just about -149 eV/atom.

Now, these authors have found that the total energy of carbon diamond is around: -9.05eV/atom.

How can I estimate total energy per atom from HF energy per atom? In case that HF energy is the estimate on Total energy, how can I find out whatever zero-energy reference my code is using and how to convert between what the package outputs and total energy?

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    $\begingroup$ How many electrons were included in your HF calculation? VASP is a pseudopotential code, so the total energy they give will neglect the contribution from the core. I also can't find the 9.05 eV in their paper with a quick search (ctrl-F) they do mention cohesive energy a lot. This isn't the same property as total energy (it's an energy difference), so what are you actually trying to find (total energy is a fairly useless quantity since we have an arbitrary choice of "0 energy"). $\endgroup$
    – Robert Lawrence
    Commented Sep 25 at 10:36

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