[Pw_forum] RE : positive Fermi energy

[BARRETEAU Cyrille]

David,
 
Ef=7.8eV is probably the right value and therefore you can plot the DOS and define Ef as the new zero of energy if you wish...
 
cyrille
 
 
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Cyrille Barreteau                                                      phone : +33 (0)1 69 08 29 51 
CEA Saclay                                                             fax :      +33 (0)1 69 08 84 46 
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De: pw_forum-bounces at pwscf.org de la part de david grifith
Date: sam. 23/10/2010 21:57
À: pw_forum at pwscf.org
Objet : Re: [Pw_forum] positive Fermi energy


   Dear Cyrille and Users

  Thanks for your answer. However, I don't want to calculate the energy of vacuum; Really I want to draw the DOS and PDOS of the BULK graphite correctly. I don't know that I should use the +7.8 eV as the Fermi energy in the DOS diagram either set it to zero and rescale the other energies or something else ?  





	  You should know that within DFT calculations the zero of energy of a periodic system is NOT the vacuum.
	




    where is the zero of energy here ? and in which way the QE chooses it ?   
  
  
 Also, can one compare this Fermi energy with the Fermi energy of another material, or  is such comparison reliable ?   





	 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
	
	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
	


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