[Pw_forum] Other ways to estimate the energy of 16 atom supercell

[Yantao Wu]

QE can calculate the energy of a 16 atom with PWscf, easily. However, I'm
looking for other ways that can confirm with the QE result, at least in
orders of magnitude.

In a fcc or bcc lattice of Fe atoms (or Cobalt or Aluminum, or potentially
any element) , for a supercell of 16 Fe atoms with periodic boundary
condition, how do you estimate the total ground state energy of the system?
By QE, the total energy is defined to include the kinetic energy of the
electrons and potential energy due to the Columbic interactions among
electron-electron, electron-nuclei, and nuclei-nuclei. The kinetic energy
of the nuclei is not included under the Born-Oppenheimer approximation.
What experimental values can be cited or theoretical calculations done to
give a rough estimate of the total energy on the order of magnitude? QE is
one way, but I want to find out other ways to confirm with the ab initio
results.

I tried to use the first a few ionization energies of Fe to estimate the
binding energy due to one atom and then multiply by 16 to get the total
energy of the system. But of course, this calculation doesn't include the
potential energy due to atom-atom interaction. Also, I was told that things
in solids dramatically change and the single-atom approximation doesn't
have much truth to it. So I'm wondering if there is a better way to make an
estimate of the total energy of the system.

Thanks in advance,
Yantao Wu
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