[Wien] Graphene bandstructure

Wed Dec 23 13:54:11 CET 2015

Dear Fhokrul
Your structure looks strange to me. The angle is 60° and not 120° and it seems that you do not take benefit of the symetry. 
Here is a cif file of graphene based on the graphite structure in which I have simply increase the c parameter. 
The structure you are using may explain why you still have a gap (symetry problem). 
Best Regards
Xavier

#======================================================================

# CRYSTAL DATA

#----------------------------------------------------------------------

data_VESTA_phase_1

_pd_phase_name                         'C'
_cell_length_a                         2.45600
_cell_length_b                         2.45600
_cell_length_c                         15.00000
_cell_angle_alpha                      90
_cell_angle_beta                       90
_cell_angle_gamma                      120
_symmetry_space_group_name_H-M         'P 63 m c'
_symmetry_Int_Tables_number            186

loop_
_symmetry_equiv_pos_as_xyz
'x, y, z'
'-y, x-y, z'
'-x+y, -x, z'
'-x, -y, z+1/2'
'y, -x+y, z+1/2'
'x-y, x, z+1/2'
'-y, -x, z'
'-x+y, y, z'
'x, x-y, z'
'y, x, z+1/2'
'x-y, -y, z+1/2'
'-x, -x+y, z+1/2'

loop_
_atom_site_label
_atom_site_occupancy
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_adp_type
_atom_site_B_iso_or_equiv
_atom_site_type_symbol
C1         1.0     0.000000      0.000000      0.000000     Biso  1.000000 C
C2         1.0     0.333333      0.666667      0.000000     Biso  1.000000 C

"Islam, Md F" <islamm at uta.edu> a écrit :

> Sorry, in my earlier email, I meant to say with 30 x 30 x 1 mesh, gap 
> is smaller but
> it doesn't close completely.
>
> Thanks,
> Fhokrul
>
>
> ________________________________________
> From: wien-bounces at zeus.theochem.tuwien.ac.at 
> [wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Islam, Md F 
> [islamm at uta.edu]
> Sent: Wednesday, December 23, 2015 6:22 AM
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] Graphene bandstructure
>
> Hi Prof Blaha,
>
>     Here is the structure I am using. I tried to be as precise as 
> possible with position coordinates.
> I think size of the vacuum is sufficiently large so that 
> supercell-supercell interaction is negligible.
> So far what I have got is that with LDA xc if I use 25 x 25 x 1 
> k-mesh there is a gap at the Fermi
> level (which passes through K point) but if I use 30 x 30 x 1 k-mesh, 
> gap closes but DOS is not
> zero at the Fermi level (about 0.001/eV). Please let me know if I am 
> doing anything wrong with
> this calculation.
>
>
> Thanks,
> Fhokrul
>
>
> Graphene
> P LATTICE,NONEQUIV.ATOMS: 2
> MODE OF CALC=RELA unit=bohr
> 4.647800 4.647800 30.000000 90.000000 90.000000 60.000000
> ATOM -1: X=0.00000000 Y=0.00000000 Z=0.50000000
>              MULT= 1 ISPLIT= 8
> C             NPT= 781 R0=0.00010000 RMT= 1.3200 Z: 6.0
> LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
>                                0.0000000 1.0000000 0.0000000
>                                0.0000000 0.0000000 1.0000000
> ATOM -2: X=0.66666667 Y=0.66666667 Z=0.50000000
>              MULT= 1 ISPLIT= 8
> C             NPT= 781 R0=0.00010000 RMT= 1.3200 Z: 6.0
> LOCAL ROT MATRIX:     1.0000000 0.0000000 0.0000000
>                                 0.0000000 1.0000000 0.0000000
>                                 0.0000000 0.0000000 1.0000000
> 12 NUMBER OF SYMMETRY OPERATIONS
> -1-1 0 0.00000000
> 0 1 0 0.00000000
> 0 0-1 0.00000000
> 1
> -1-1 0 0.00000000
> 0 1 0 0.00000000
> 0 0 1 0.00000000
> 2
> -1-1 0 0.00000000
> 1 0 0 0.00000000
> 0 0-1 0.00000000
> 3
> -1-1 0 0.00000000
> 1 0 0 0.00000000
> 0 0 1 0.00000000
> 4
> 0 1 0 0.00000000
> -1-1 0 0.00000000
> 0 0-1 0.00000000
> 5
> 0 1 0 0.00000000
> -1-1 0 0.00000000
> 0 0 1 0.00000000
> 6
> 0 1 0 0.00000000
> 1 0 0 0.00000000
> 0 0-1 0.00000000
> 7
> 0 1 0 0.00000000
> 1 0 0 0.00000000
> 0 0 1 0.00000000
> 8
> 1 0 0 0.00000000
> -1-1 0 0.00000000
> 0 0-1 0.00000000
> 9
> 1 0 0 0.00000000
> -1-1 0 0.00000000
> 0 0 1 0.00000000
> 10
> 1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0-1 0.00000000
> 11
> 1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0 1 0.00000000
> 12
>
>
>
>
> ________________________________________
> From: wien-bounces at zeus.theochem.tuwien.ac.at 
> [wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha 
> [pblaha at theochem.tuwien.ac.at]
> Sent: Tuesday, December 22, 2015 3:29 PM
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] Graphene bandstructure
>
> The two eigenvalues at K must be identical by symmetry.
>
> If you have a splitting of some meV it means that your structure is
> slightly wrong.
>
> Typical errors: positions of 1/3 and 2/3 must be given in full precision.
>   0.3333   is NOT 1/3
>
> Am 22.12.2015 um 20:31 schrieb Islam, Md F:
>> Hi Prof Blaha,
>>
>>      I have got the gap from plotting bandstructure as well as DOS 
>> calculations.
>> I can see the linear dispersion at the K point just like the way it 
>> is suppose to be
>> when I plot all the bands in eV range. But if I zoom in at the K 
>> point in meV range,
>> I can see the gap.
>>
>>     I don't think there is anything wrong with the structure. I did 
>> check all bond lengths,
>> angles before I ran the calculations and they are correct. I suspect 
>> I may have to adjust
>> parameters. I started to see some difference with LDA xc functional 
>> with larger k mesh.
>>
>>
>> Thanks,
>> Fhokrul
>>
>>
>>
>>
>> ________________________________________
>> From: wien-bounces at zeus.theochem.tuwien.ac.at 
>> [wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha 
>> [pblaha at theochem.tuwien.ac.at]
>> Sent: Tuesday, December 22, 2015 11:35 AM
>> To: A Mailing list for WIEN2k users
>> Subject: Re: [Wien] Graphene bandstructure
>>
>> Graphene is metallic by "symmetry", i.e. EF is at a 2-fold eigenvalue at
>> the K-point and bands cross with a linear dispersion.
>>
>>   From where do you know that graphene has a gap in your calculations ??
>>
>>   From :gap in the scf file or from plotting the bandstructure or ...
>>
>> It the state at K is not degenerate, you have the wrong symmetry and are
>> not doing graphene.
>>
>> Am 22.12.2015 um 16:51 schrieb Islam, Md F:
>>> Hi,
>>>
>>>        I am trying to do a bandstructure calculation of graphene to 
>>> check if I can
>>> reproduce results discussed in literature (I am using a unit cell 
>>> of 2 atoms).
>>> With spin-orbit coupling, there should be a gap of the order of few 
>>> micro-eV
>>> and without spin-orbit, there should not be any gap at Dirac point. 
>>> But I am
>>> getting a gap of meV even without spin-orbit. I tried both GGA and LDA with
>>> very dense mesh but the gap does not close. So I am wondering if anyone
>>> have any suggestion about how to do it in Wien2k.
>>>
>>>
>>> Thanks,
>>> Fhokrul
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>> SEARCH the MAILING-LIST at:  
>>> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>>>
>>
>> --
>> --------------------------------------------------------------------------
>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
>> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
>> WWW:   http://www.imc.tuwien.ac.at/staff/tc_group_e.php
>> --------------------------------------------------------------------------
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>
> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
> WWW:   http://www.imc.tuwien.ac.at/staff/tc_group_e.php
> --------------------------------------------------------------------------
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