Nicolas, Even though formally your system is semimetallic, whether or not you get that character right in a calculation would depend on your k-point sampling relative to the size of the system. Or if there is a particular point which is special, you might need to make sure that you are effectively considering that point in the sampling.
Alberto On Sun, Mar 28, 2010 at 2:33 PM, Nicolas Leconte <[email protected]> wrote: > 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 <[email protected]> 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 >> > <[email protected]>wrote: >> > >> >> Hello Alberto, >> >> >> >> Thanks for your answer. Comments below... >> >> >> >> On Thu, Mar 11, 2010 at 4:12 PM, Alberto Garcia <[email protected]> >> >> 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 >> >>> <[email protected]> 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:[email protected] >> ...............................................:[email protected] >> 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:[email protected] >> ...............................................:[email protected] >> http://www.iitk.ac.in/phy/People/phy_facvis.html >> http://www.iitk.ac.in/phy/New01/profile_SA.html >> ....................................................................... >> ~ > >
