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

[Robert Hembree]

Dear Shamsu

 

Your input file and parameters are fine. When you plot the DOS you need to
shift your  Fermi level to zero if you want the gap to show up at zero. 

Add the line

verbosity = 'high' 

to the control part of your input file and run pw.x again. Then you can grep
your output file

less scf.out | grep 'Fermi energy'

 

You should get a line that looks like this:

the Fermi energy is    -1.6709 ev

 

When you plot your DOS, for instance in gnuplot you would now plot

 

plot 'Graph01.dos' ($1-(-1.6709)):2 w l

and you should see your  plot with the bandgap and dispersion at zero. 

 

When you do these calculations the Fermi level will rarely show up at
exactly zero.

 

Robert

 

From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of Shamsu Abubakar
Sent: Wednesday, April 03, 2013 8:23 PM
To: pw_forum at pwscf.org
Subject: [Pw_forum] Fermi energy reference point shift from 0 to -2

 

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 Physics

University Putra Malaysia

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