Vasp stresses are confusing and unit is a mystery

[Leimeroth]

Lammps and vasp stores pressures/stresses somehow different and vasp stresses are confusing. Default lammps jobs store pressures as full matrix and stress =-pressure. For vasp the output contains a 3 vector pressure and a matrix stresses, but the stresses do not give any reasonable result when trying to caculate elastic constants with them and a short look in the code made me assume that units are not the same as for pressures.

[pmrv]

Yes, the current value of pressures makes no sense, I introduced stresses for backwards-compat, but it's been a while and imo we can throw the old pressures out. I'm not sure about the unit off the top my head, but I've used the stress output before successfully.

[Leimeroth]

To get stresses from the format written in hdf to GPa (which is the pyiron unit for pressure, so it makes sense for stresses too imo) I need to stress = stress/KBAR_TO_EVA*0.1