Top Page > Browsing

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 Re: Fermi level is not at the middle of the gap ( No.3 ) Date: 2011/08/26 14:37 Name: Yasutaka Nishida Dear Professor T. Ozaki and OPENMX users. I have begun to learn about first principles calculation, so I am just a beginner. I have same question about the above mentioned. If we take lim T->0 (scf.ElectronicTemperature) in a input file, can we consider that the chemical potential calculated by OpenMX corresponds to the Fermi level? Then, Is the Fermi level taken to be the middle in the gap? Sincerely, Yasutaka Nishida. Re: Fermi level is not at the middle of the gap ( No.4 ) Date: 2011/08/26 17:43 Name: T.Ozaki Hi, > If we take lim T->0 (scf.ElectronicTemperature) in a input file, > can we consider that the chemical potential calculated by OpenMX > corresponds to the Fermi level? The above statement is correct only for metallic systems. > Then, Is the Fermi level taken to be the middle in the gap? If there is a gap between valence and conduction bands, the Fermi level can be any energy in between the top of valence and the bottom of conduction bands at T=0. So, the chemical potential calculated by OpenMX at a low temperature may not be at the middle of the gap even for a very low temperature. If you want to take the Fermi level to be the middle of the gap for that case, you can adjust it as you like. Regards, TO

Page: [1]