Band offsets

[emilgojny]

Dear ABINIT users,

I've been using ABINIT for some time now with great success but now I stumbled on a problem.

How to calculate band offsets of two semiconductor alloys? I tried to calculate it for an experimentally known situation (GaAs and GaSb) where the difference in Conduction Band energy should be about -0.1eV and the difference in Valence Band energy should be about 0.5eV (all in gamma point of course).

I got 1.5eV and 2.1eV. The whole GaSb band structure seems to be shifted upwards for about 1.6eV.

I used the Tran and Blaha correction to modified Becke Johnson functional (TB09 mBJLDA), the band gaps and overall shapes of band structures are excellent, its just the offsets between the two systems that are off.

This is understandable, since there is no reference level (vacuum) in an infinite crystal. But how does ABINIT scale the energies? What is the reference? Is there a possibility to force it to scale to the same level for both calculations? Or maybe there is an other way to calculate band offsets?

I would appreciate all your answers and suggestions

Emil G.