Hello S. Auluck, Thank you for your answer. But as mentioned to Alberto, my system is still semi-metallic (bandgap crossing not far from K k-point), so no bandgap is present... I will do some tests on pure graphene to see if the problem occurs there too.
Nicolas On Sun, Mar 28, 2010 at 9:50 AM, Sushil Auluck <saul...@iitk.ac.in> wrote: > hi, > > in a semi-conductor or insulator there is a energy gap. in this region the > dos is zero. so in principle E_f can be placed anywhere in between because > E_f is determined by the integral of N(E)dE from zero to E_f which must > give the total number of valence electrons. > it depends on the conditions (type of broadening & amount of broadening) > used in the code. i encountered such situations in wien2k code. > > s.auluck > > > Sorry to bump this up again, but this issue still puzzles me... > > > > Thanks in advance, > > Nicolas > > > > On Mon, Mar 22, 2010 at 4:02 PM, Nicolas Leconte > > <lecontenico...@gmail.com>wrote: > > > >> Hello Alberto, > >> > >> Thanks for your answer. Comments below... > >> > >> On Thu, Mar 11, 2010 at 4:12 PM, Alberto Garcia <alber...@icmab.es> > >> wrote: > >> > >>> Nicolas, > >>> > >>> There are two possible reasons for the differences. > >>> > >>> 1. If the system is an insulator, the placement by Siesta of the Fermi > >>> level is rather arbitrary: you can count on it being in the gap, but > >>> the actual > >>> location will depend on how many states you start with in the > >>> bisection algorithm used. Mprop uses a different algorithm. In this > >>> case the physics > >>> does not depend on the location, as long as it is in the gap. > >>> > >> > >> My system is not an insulator : it's functionnalized graphene with a > >> shifted band crossing at the Dirac point (somewhere on the path between > >> K' > >> and \Gamma). So it is still semi-metallic. > >> > >> Or does the mere fact I am calculating with SIESTA the wave-functions > >> (.WFSX input to be used with mprop) at the \Gamma point only interferes > >> somehow in the algorithm? > >> > >> > >>> > >>> 2. In general, mprop will work with a certain (gaussian) smearing. > >>> Siesta would have used typically a Fermi-Dirac smearing, according to > >>> the electronic temperature specified. If you use a more or less > >>> equivalent smearing in mprop, you should get similar values for the > >>> Fermi level. > >>> > >> > >> If point 1 does not concern me, it should be related to this point. But > >> it > >> does not fix the issue : > >> > >> - In the .EIG file of the SIESTA run, my electronic temperature is > >> 350 > >> K (which corresponds roughly to 0.03 eV). I obtain a Fermi energy > >> energy of > >> -4.7 eV. > >> - In the .stt file after mprop post-processing with the same 0.03 eV > >> smearing, I obtain a Fermi energy value of -6.4 eV. > >> > >> The discrepancy between the two values is still considerable. > >> > >> Any other comments/ideas? > >> > >> Thanks in advance, > >> Nicolas > >> > >> > >>> Alberto > >>> > >>> > >>> On Thu, Mar 11, 2010 at 9:52 AM, Nicolas Leconte > >>> <lecontenico...@gmail.com> wrote: > >>> > Hello, > >>> > Quick question. Is there a particular reason the Fermi energy value > >>> obtained > >>> > by a regular SIESTA calculation in the *.EIG file is different in > >>> absolute > >>> > value from the one found in the .stt file after a COOP analysis with > >>> the > >>> > mprop executable in the Util directory? > >>> > Thanks in advance, > >>> > Nicolas > >>> > >> > >> > > > > > > > ....................................................................... > Prof. Sushil Auluck Phone:+91-512-6797092/6148 > Department of Physics +91-512-6798177(Home) > Indian Institute of Technology Cell :+91-9305548667 > Kanpur 208016 (UP) Fax :+91-512-6790914 > India > E-mail:saul...@iitk.ac.in<e-mail%3asaul...@iitk.ac.in> > ...............................................:saul...@gmail.com > http://www.iitk.ac.in/phy/People/phy_facvis.html > http://www.iitk.ac.in/phy/New01/profile_SA.html > ....................................................................... > ~ > > ....................................................................... > Prof. Sushil Auluck Phone:+91-512-6797092/6148 > Department of Physics +91-512-6798177(Home) > Indian Institute of Technology Cell :+91-9305548667 > Kanpur 208016 (UP) Fax :+91-512-6790914 > India > E-mail:saul...@iitk.ac.in<e-mail%3asaul...@iitk.ac.in> > ...............................................:saul...@gmail.com > http://www.iitk.ac.in/phy/People/phy_facvis.html > http://www.iitk.ac.in/phy/New01/profile_SA.html > ....................................................................... > ~ >
