[DFTB-Plus-User] Fermi energy for surface

[Vladimir Yushkevich]

Dear dftb+ users,



I have following issue. My system is slab of titanium dioxide surface and I
have found that by increasing the supercell size in nonpereodic direction
(increasing the thickness of vacuum layer between two repeated slabs) the
obtained Fermi energy also increases. In slab approximation the vacuum layer
should be thick enough but I really confused in choice of it. The slab
thickness is ~ 16 Å and for two different supercell heights of ~50 Å and
~100 Å the corresponding Fermi energies are 3.2 eV and 3.6 eV respectively.
Of cause for supercell height >100 Å the convergence in Fermi energy is
better but in literature I didn’t found so thick vacuum layers. Such
difference is not so pronounced for total energy (~2E-5 eV).



Best regards, Vladimir
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