[CP2K-user] Fermi energy too high?

Matt W mattwa... at gmail.com
Fri Dec 14 16:41:03 UTC 2018

In a periodic system the zero of the one electron levels is arbitrary. If 
you need a reference you need to run a slab calculation with vacuum or try 
to align semi-core states to something.


On Friday, December 14, 2018 at 4:33:13 PM UTC, Phil G. wrote:
> Dear people and experts of CP2K,
> after the geometry optimization of the lithium niobate (LiNbO3) unit cell 
> I would like to obtain pdos in order to determine the band gap and Fermi 
> energy of the bulk system.
> After the calculation with ENERGY_FORCE I got pdos files of the three 
> atoms (indexing depends on the z-position of the atoms) and I'm wondering 
> about the value of Fermi energy: E_F = 0.300174 a.u. which is 8.168 eV. Is 
> that not too high? And which energy has the value 0 and what is the 
> reference? What is the Fermi energy defined in the language of CP2K?
> The energy band gap (HOMO-LUMO gap) of 3.62 eV agrees well with 
> experimental values of 3.7 to 3.9 eV. But I cannot imagine that Fermi level 
> has too high energy values.
> Has anyone an idea what is the reason for such high Fermi energy values?
> Here the input and output files are attached here.
> Kind regards,
> Phil
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