Fermi level is not at the middle of the gap

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Fermi level is not at the middle of the gap

Date: 2009/09/29 09:59
Name: Dinh Loc Duong <mambom1902@yahoo.com>: Dear Prof.T.Ozaki and OPENMX users,

I try to draw the bandstructure of CNT but I have a problem. The fermi level is inside the gap but not at the middle of the gap.

In general, in the case of semiconducting tube, the feri level shoulb be at the middle of the gap. I see the example of Diamond in manual, Fermilevel is also not the middle of the gap.

My question is what the definition of Fermi level in OPENMX. In the case of semicondutor, can I set up by hand to be consistent with the general concept( set Fermi level at the middle of the gap)?

I great appreciate your help.

Sincerely,
Dinh Loc Duong.

Page: [1]

Re: Fermi level is not at the middle of the gap ( No.1 )

Date: 2009/09/30 11:48
Name: T.Ozaki

Hi,

What OpenMX gives is not Fermi level (EF), but chemical potential(mu) for a given
temperature (T). The mu is found in OpenMX so that the total number of electrons
can be conserved at T. Also, we have a relation:

lim T->0 mu = EF

Thus, you may consider that the chemical potential mu at T=0K does correspond to
the Fermi level. However, the quantity for a gap system is not well defined,
since the Fermi function becomes a step function at 0K. This implies that any energy
in the gap can satisfy the condition of the charge conservation.
Therefore, the Fermi level is taken to be the middle in the gap in text books
as convention.

In general cases for finite temperature, the chemical potential can vary from the
middle of gap depending on the shape of DOS. This is exactly the cases of diamond
and your CNT.

Regards,

TO

Re: Fermi level is not at the middle of the gap ( No.2 )

Date: 2009/10/16 09:39
Name: Dinh Loc Duong <mambom1902@yahoo.com>

I appreciate for your reply.

Sincerely,
Dinh Loc Duong

Page: [1]