How to determine fermi level in DOS calculation of a bulk crystallite

[lamha]

Hi all,
I am a newbie of VASP, what I am trying to do is to calculate the DOS of a crystallite insulator, in presence of some defects.
But I don't know how to exactly fermil level because everytime I restart my calculation, the position of DOS shifts over the energy range although the relative value of energy remains the same. I read the thread http://cms.mpi.univie.ac.at/vasp-forum/ ... php?4.7385
But I do not really understand. I heard the the reference energy may be computed from the electrostatic potential, but I don't know how.
Anybody having experience on this issue can give me a hand?
Thank you very much

[tlchan]

what I am trying to do is to calculate the DOS of a crystallite insulator, in presence of some defects. But I don't know how to exactly fermil level because everytime I restart my calculation, the position of DOS shifts over the energy range although the relative value of energy remains the same.

If your calculations have exactly the same input parameters, the DOS shouldn't shift. Probably, something is different between the calculations.

I heard the the reference energy may be computed from the electrostatic potential, but I don't know how.

If your system has a surface, you can use the potential in the vacuum as the reference. If you want to align the band structures of two systems (for example, a crystal with defect and the bulk crystal), you can pick a bulk-like atom in the defect system and a corresponding atom in the bulk system, and align the potentials on the two atoms without explicitly choosing a reference energy.