[Pw_forum] Definition of Fermi level in PWscf

Paolo Giannozzi giannozz at democritos.it
Mon Apr 13 22:29:16 CEST 2009

On Monday 13 April 2009 02:32, loc duong ding wrote:

> I wonder what is the critical of choosing Fermi level in Pwscf algorithm?

and I wonder what you mean.

The Fermi energy calculated by PWscf for an insulator can be anywhere in 
the gap. Its exact location is unpredictable, irrelevant, and has no meaning
anyway. The phisical Fermi energy for intrinsic semiconductors is located 
in the middle of the band gap (this is a textbook problem, by the way).

> By the way, Fermi level is  equal to the chemical potential at 0K. So, It
> is a very important physical meaning and it must be a specific value at
> 0K in metal, semiconductor and insulator. 

the Fermi energy for metals is correctly calculated (within the chosen
approximation). For semiconductors and metals, see above

Paolo Giannozzi, Democritos and Udine University

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