Dear Eduardo Let me precise a little this point. If you do a fixed total moment calculation as explained by Lorenzo you get two different Fermi energies. You can also plot E(M) ie the total energy with respect to the total magnetization. You will then find a minimum of energy (or several ones if you have metastable solutions) for a given M0. This M0 corresponds to the true ground state and for this particular case the two Fermi energies are aligned.. hth cyrille ================================================================== Cyrille Barreteau phone : +33 (0)1 69 08 29 51 CEA Saclay fax : +33 (0)1 69 08 84 46 IRAMIS, SPCSI, Batiment 462 email cyrille.barreteau at cea.fr 91191 Gif sur Yvette Cedex FRANCE ~~~~~~~~~~~~~~~~~~~~~~~~ Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/ ==================================================================
________________________________ De: pw_forum-bounces at pwscf.org de la part de Lorenzo Paulatto Date: jeu. 21/04/2011 11:00 ?: PWSCF Forum Objet : Re: [Pw_forum] why are there two Fermi energies? On Thu, 21 Apr 2011 01:35:39 +0200, Eduardo Ariel Menendez Proupin <eariel99 at gmail.com> wrote: > Why are there two Fermi energies in certain spin-polarized calculations ? > > input starting_magnetization(1) = 0.0, > starting_magnetization(2) = 0.5, > output the Fermi energy is 6.1598 ev > ! total energy = -502.92538790 Ry > > input tot_magnetization = 1 > output the spin up/dw Fermi energies are 6.3821 6.1598 ev > ! total energy = -502.92538790 Ry > > What is the meaning of the spin up Fermi level in the second case? Dear Eduardo, if you force the system to have a certain magnetization (i.e. setting tot_magnetization) you are actually asking to occupy the "up" spin orbital more then the "down" spin ones, i.e. you have more up electrons then down electrons. This is achieved by filling the up orbitals up to a higher energy than the down orbitals, by setting two distinct Fermi energies. On the other hand, if you only set starting magnetization, you get the computational ground state, where up and down orbitals are be filled up to the same level; what changes is the KS eigenvalues. hth, lorenzo > > This numbers are for a 64 atoms Si unit cell with one Si replaced by Al, > and > only one k-point, but the same happens with more k-points. I also used > Fermi > smearing with a very low smearing. > There is a difference if I set the starting magnetization or the total > magnetization, with pw.x version 4.2.1. However, despite reporting > different > Fermi levels, the total energy and magnetization are equal. Also are > equal > KS energies, at least around the Fermi levels. > > Thanks, > > Eduardo Menendez > Departamento de Fisica > Facultad de Ciencias > Universidad de Chile > Phone: (56)(2)9787439 > URL: http://fisica.ciencias.uchile.cl/~emenendez -- Lorenzo Paulatto (IdR) IMPMC - CNRS UMR 7590 & Universit? P&M Curie T23-C23/24-4e16 - 4 place Jussieu - 75252 Paris Cedex5 phone: +33 (0)144 27 5211 www: http://www-int.impmc.upmc.fr/~paulatto/ _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/ms-tnef Size: 8646 bytes Desc: not available Url : http://www.democritos.it/pipermail/pw_forum/attachments/20110421/d6eee42b/attachment-0001.bin