[Pw_forum] RE : positive fermi energy

[BARRETEAU Cyrille]

David,
 
You should know that within DFT calculations the zero of energy of a periodic system is NOT the vacuum. If you want to get the energy of vacuum you can simulate for example a surface with the "supercell" method  ie including empty space between slabs. You will get the vacuum energy (and therefore also the work function) by plotting the potential far away from you slabs in the "empty" region.
 
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 david grifith
Date: sam. 23/10/2010 13:59
À: PwSCF Forum
Objet : [Pw_forum] positive fermi energy


Dear All
 
I get positive fermi energy (+7.8 eV) for bulk graphite by Quantum Espresso. Positive energy is meaningless for me here. Would you please say me that in whcih way QE selects the zero energy?
As I know the vacuum should be considered as zero energy.  I appreciate you in advance to solve the problem.

-- 
Sincerely Yours
David G.
JCU


-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/ms-tnef
Size: 5742 bytes
Desc: not available
Url : http://www.democritos.it/pipermail/pw_forum/attachments/20101023/b353be7d/attachment.bin