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 >> > >
