[Pw_forum] A little energy gap (~ 0.2 eV) for graphene

[PJ Ren]

Dear Cao,
I am new to graphene calculation, and there is some questions about your 
input files.
First, why do you use rectangular cell, not a trigonal primary cell?
Second, is it necessary to consider the magnetization of graphene? Can 
you share some paper on this?
Thanks very much.

Pengju Ren

Dalian Institute of Chemical Physics, CAS


On 05/21/2012 08:13 PM, Cao TF wrote:
> Dear QE users,
> I have calculated the density of states (DOS) of pure graphene. The 
> supercell used in my work is a rectangular cell containing 60 carbon 
> atoms. But something has puzzled me greatly. There is always a little 
> energy gap (~0.2 eV) in the DOS, which contracts with the fact that 
> graphene is zero gap semiconductor. Although I have change many 
> parameters. This problem has not been solved. Here I give the input 
> file and I will be greatly appreciated if you can give me some 
> suggestions.
> For scf.in
> &CONTROL
> title = 'graphene layer' ,
> calculation = 'scf' ,
> restart_mode = 'from_scratch' ,
> outdir = './tmp' ,
> pseudo_dir = '~pseudo' ,
> prefix = 'graphene' ,
> /
> &SYSTEM
> ibrav = 8 ,
> a = 12.31 , b = 12.79312342 , c = 12.000 ,
> nat = 60 ,
> ntyp = 1 ,
> occupations = 'smearing' ,
> tot_charge = 0.0,
> degauss = 0.02 ,
> smearing = 'mp' ,
> nspin = 2 ,
> starting_magnetization(1) = 0.5 ,
> ecutwfc = 30.0 ,
> ecutrho = 300.0 ,
> /
> &ELECTRONS
> conv_thr = 1.0d-8 ,
> mixing_mode = 'local-TF' ,
> mixing_beta = 0.7 ,
> diagonalization = 'david' ,
> /
> ATOMIC_SPECIES
> C 12.0107 C.pbe-rrkjus.UPF
> ATOMIC_POSITIONS crystal
> C 0.0000000 0.0000000 0.50000000
> C 0.10000000 5.55555671E-02 0.50000000
> C 0.10000000 0.16666667 0.50000000
> C 0.0000000 0.22222224 0.50000000
> C 0.0000000 0.33333334 0.50000000
> C 0.10000000 0.38888890 0.50000000
> C 0.10000000 0.50000000 0.50000000
> C 0.0000000 0.55555558 0.50000000
> C 0.0000000 0.66666669 0.50000000
> C 0.10000000 0.72222227 0.50000000
> C 0.10000000 0.83333337 0.50000000
> C 0.0000000 0.88888896 0.50000000
> C 0.20000000 0.0000000 0.50000000
> C 0.30000001 5.55555671E-02 0.50000000
> C 0.30000001 0.16666667 0.50000000
> C 0.20000000 0.22222224 0.50000000
> C 0.20000000 0.33333334 0.50000000
> C 0.30000001 0.38888890 0.50000000
> C 0.30000001 0.50000000 0.50000000
> C 0.20000000 0.55555558 0.50000000
> C 0.20000000 0.66666669 0.50000000
> C 0.30000001 0.72222227 0.50000000
> C 0.30000001 0.83333337 0.50000000
> C 0.20000000 0.88888896 0.50000000
> C 0.40000001 0.0000000 0.50000000
> C 0.50000000 5.55555671E-02 0.50000000
> C 0.50000000 0.16666667 0.50000000
> C 0.40000001 0.22222224 0.50000000
> C 0.40000001 0.33333334 0.50000000
> C 0.50000000 0.38888890 0.50000000
> C 0.50000000 0.50000000 0.50000000
> C 0.40000001 0.55555558 0.50000000
> C 0.40000001 0.66666669 0.50000000
> C 0.50000000 0.72222227 0.50000000
> C 0.50000000 0.83333337 0.50000000
> C 0.40000001 0.88888896 0.50000000
> C 0.60000002 0.0000000 0.50000000
> C 0.70000005 5.55555671E-02 0.50000000
> C 0.70000005 0.16666667 0.50000000
> C 0.60000002 0.22222224 0.50000000
> C 0.60000002 0.33333334 0.50000000
> C 0.70000005 0.38888890 0.50000000
> C 0.70000005 0.50000000 0.50000000
> C 0.60000002 0.55555558 0.50000000
> C 0.60000002 0.66666669 0.50000000
> C 0.70000005 0.72222227 0.50000000
> C 0.70000005 0.83333337 0.50000000
> C 0.60000002 0.88888896 0.50000000
> C 0.80000001 0.0000000 0.50000000
> C 0.90000004 5.55555671E-02 0.50000000
> C 0.90000004 0.16666667 0.50000000
> C 0.80000001 0.22222224 0.50000000
> C 0.80000001 0.33333334 0.50000000
> C 0.90000004 0.38888890 0.50000000
> C 0.90000004 0.50000000 0.50000000
> C 0.80000001 0.55555558 0.50000000
> C 0.80000001 0.66666669 0.50000000
> C 0.90000004 0.72222227 0.50000000
> C 0.90000004 0.83333337 0.50000000
> C 0.80000001 0.88888896 0.50000000
> K_POINTS automatic
> 8 8 1 0 0 0
> For nscf.in
> &CONTROL
> title = 'graphene layer' ,
> calculation = 'nscf' ,
> restart_mode = 'from_scratch' ,
> outdir = './tmp' ,
> pseudo_dir = '/lustre/ISSP2/tfcao/pseudo' ,
> prefix = 'graphene' ,
> /
> &SYSTEM
> ibrav = 8 ,
> a = 12.31 , b = 12.79312342 , c = 12.000 ,
> nat = 60 ,
> ntyp = 1 ,
> occupations = 'tetrahedra' ,
> tot_charge = 0.0,
> nspin = 2 ,
> starting_magnetization(1) = 0.5 ,
> ecutwfc = 30.0 ,
> ecutrho = 300.0 ,
> /
> &ELECTRONS
> conv_thr = 1.0d-8 ,
> mixing_mode = 'local-TF' ,
> mixing_beta = 0.7 ,
> diagonalization = 'david' ,
> /
> ATOMIC_SPECIES
> C 12.0107 C.pbe-rrkjus.UPF
> For dos.in
> &inputpp
> prefix = 'graphene' ,
> outdir = './tmp' ,
> Emin = -4.0 ,
> Emax = 4.0 ,
> DeltaE = 0.01 ,
> fildos = graphene.dos ,
> /
> The accessory is the DOS I have got.
> I am sorry for such a long file. I hope that you can give some 
> suggestions.
> ======================================================================
> Tengfei Cao, Research Laboratory for Computational Materials Sciences,
> Instutue of Solid State Physics,the Chinese Academy of Sciences,
>
> ======================================================================
>
>
>
>
>
>
> 93,2 ??
> 1,2 ??
>
>
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