[Pw_forum] Fermi energy reference point shift from 0 to -2

[Shamsu Abubakar]

Dear Q.E Users.
I have a system of 4x4 graphene supercell, comprising 32 carbon 
atoms. I sucessfully run all the calculations i.e scf,nscf and other 
postprocessing such as DOS and PDOS. But the main problem i'm facing 
currently is on the density of state. Usually, i consider zero to be my 
fermi reference energy point in my ./dos.x input file, forexample,from 
-10 and 10 as my Emin and Emax respectivily. For pristine graphene,i 
expect to always see the dispersion at the zero vicinity, showing a semi metallic behavior, but surprisingly, its always moving 
away from zero to around -2, in the valence band side which i knew is unsual for pristine graphene. However, when i combine graphene with GaAs nanostructure, most of the interesting properties interms of orbitals contributions (PDOS), also resides on similar point -2. That is some of the contributions 
that are supposed to be seen at the vicinity of the fermi level, now 
moved to another point -2. Also, i consider changing the smearing from 
marzari-vanderbilt to Fermi- Dirac, but similar 
properties were observed. I decided to consider only 1x1, and 2x2 
graphene supercell alone, still similar properties i observed also. In 
fact, i even consider changing my pseudopotential from pw91 to 
pbe.rrkjus still no progress. My 
problem now, i don't know what really causes these shift from 0 to -2. 

I attached one of my graphene scf input file for your verification and advice.

 &CONTROL
                    title = 'Graphene monolayer01',
                      prefix = 'Graph01',
                 calculation = 'scf' ,
                restart_mode = 'from_scratch'
 ,
                     outdir = '/home//???/espresso-4.1.2/bin/' ,
                  pseudo_dir = '/home//???/???/espresso-4.1.2/upf_files/' ,
               
                     tstress = .true. ,
                     tprnfor = .true.
 ,
 /
 &SYSTEM
                       ibrav = 4,
                   celldm(1) = 18.59490373,
                   celldm(3) = 1.80,
                         nat = 32,
                        ntyp = 1,
                     ecutwfc = 34.D0
 ,
                  tot_charge = 0.000000,
                 occupations = 'smearing' ,
                     degauss = 0.02 ,
                    smearing = 'fermi-dirac' ,
                     
 /
 &ELECTRONS
                    conv_thr = 1.D-8 ,
                 mixing_beta = 0.7D0
 ,
 /
ATOMIC_SPECIES
     C   12.00000  C.pw91-van_ak.UPF 
    
ATOMIC_POSITIONS (angstrom)
C        1.229999657   0.709326753   1.999999753
C        2.459999165   1.419486000   1.999999874
C        3.689999208   0.709327391   1.999999822
C        4.920000000   1.419486496   1.999999944
C        4.920000000   2.839880146   2.000000125
C        6.149999990   3.549976521   1.999999907
C        3.690000010   3.549976521   1.999999907
C       
 2.459999764   2.839879152   2.000000067
C        6.150000792   0.709327391   1.999999822
C        7.380000835   1.419486000   1.999999874
C        7.380000236   2.839879152   2.000000067
C        8.610000005   3.549975943   1.999999891
C        8.609999654   4.970023341   2.000000208
C        9.840000000   5.680120078   2.000000200
C        7.379999382   5.680120770   2.000000152
C        6.149999800   4.970024086   2.000000150
C       
 4.920000000   5.680121474   2.000000132
C        3.690000200   4.970024086   2.000000150
C        8.610000343   0.709326753   1.999999753
C        9.840000000   1.419485253   1.999999874
C        9.840000000   2.839878353   2.000000070
C       11.069999995   3.549975943   1.999999891
C       11.070000346   4.970023341   2.000000208
C       12.300000618   5.680120770   2.000000152
C       12.300001137   7.100514050   2.000000166
C       13.530000464  
 7.810673002   1.999999744
C       11.070000830   7.810672948   1.999999928
C        9.840000000   7.100514025   2.000000287
C        8.609999170   7.810672948   1.999999928
C        7.379998863   7.100514050   2.000000166
C        6.149999536   7.810673002   1.999999744
C        4.920000000   7.100514261   2.000000041
      
K_POINTS automatic 
  6 6 1   0 0 0 

Thank you for your kind response.

Shamsu Abubakar
Postgraduate student

Department of PhysicsUniversity Putra Malaysia
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20130404/e62a3c04/attachment.html>