Bulk potential energy by different methods

[Sebastian Hütter]

Hi all,

this may be a simple question, but somehow I feel like I am missing 
something very basic here.

I'm simply comparing bulk energies of metals (here: Al) computed over 
XYZ-periodic unit cells obtained via DFT in cp2k and several EAM potentials 
in LAMMPS. Different published potentials in LAMMPS all agree on an energy 
of somewhere around -14 eV/unit cell. However, when I run the same 
computation in cp2k (input file attached), I find energies (printed as the 
"FORCE_EVAL ( QS ) energy") of -8.3 Ha/unit cell, or -226 eV/unit cell. As 
this is more than one order of magnitude off, something can't be right here.
To see if the relative energies are usable, I then tried to calculate 
vacancy formation energy by comparing the supercell energies with and 
without vacancies (cf. 
https://icme.hpc.msstate.edu/mediawiki/index.php/LAMMPS_Vacancy_Formation_Energy) 
, but that is wrong as well, while the LAMMPS solution agrees reasonably 
well with experimental data.

It appears as if every energy value calculated is too large by a factor of 
16? Why would that be the case?


Thank your for your help,

Sebastian
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