Dr S Bailey Physics Department Lancaster University Lancaster, UK. LA1 4YB Tel. +44(0)1524592844 -----Original Message----- From: Siesta, Self-Consistent DFT LCAO program, http://www.uam.es/siesta [mailto:[EMAIL PROTECTED] On Behalf Of Andrei Postnikov Sent: 11 January 2007 09:05 To: SIESTA-L@listserv.uam.es Subject: Re: [SIESTA-L] Fermi level and k-grid On Wed, 10 Jan 2007, Oleksandr Voznyy wrote: | > The Fermi level is normally calculated by setting the cumulative | > occupation number of all bands to the number of valence electrons. | | As I understand this means that Ef in semiconductor would always be at | the VBM and not in the middle of the gap? Alexander - sorry, it seems that I was wrong. I just checked my old calculation for a wide-gap dielectric and see that Fermi energy = -6.866874 eV while the energies bordeing the gap -8.08 and -4.66. One should look into details of implementation... Yes in other band structure codes I know the Fermi energy is fixed by the last occupied band, i.e. it is set at the valence band top. Then if it technically lies higher, this must be due to the energy broadening introduced. But apparently in Siesta it is done differently. | By the way, how the bandstructure is calculated using only several k-points? The band structure as such (continuous bands) is not calculated, each k-point enters independently of others and contributes a (smeared) peak in the density of states. This summary DOS is (roughly speaking) integrated, and as the number of electrons is achieved, the Fermi level is set. (The details of implementation might be different). Best regards, Andrei +-- Dr. Andrei Postnikov ---- Tel. +33-387315873 ----- mobile ++33-666784053 ---+ | Paul Verlaine University - Institute de Physique Electronique et Chimie, | | Laboratoire de Physique des Milieux Denses, 1 Bd Arago, F-57078 Metz, | France | +-- [EMAIL PROTECTED] ------------ +http://www.home.uni-osnabrueck.de/apostnik/ --+
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