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I have done two calculations for systems AX and BX using the same augmentation energy. Is the following definition of the band offset correct?

Bandoffset = (VBM(AX) - avpot(X)) - (VBM(BX)-avpot(BX))

where I use the notation

VBM (AX) = valence band maximum of AX

avpot (X) = average electrostatic potential at atom X
<span class='smallblacktext'>[ Edited ]</span>

in principle the expression for the band offset is correct. However, the 'average potential' itself is only defined to within a constant offset in 3D periodic bulk cells. However, if you have a slab (with a vacuum region in the unit cell), this can be overcome by referring the potentials to the 'vacuum potential' (if the vacuum is sufficiently thick) (set LVTOT=.true. and refer all energies to the vacuum potential)

Dear Admin, as I have a kind of oxide, such as HfO2, I try try to align the VBM of two different charge states, neutral and single positively charged.
my problem is that how can I get the average electron-static potential, since there are two kinds of atoms.
Thanks a lot.