[Wien] Graphene bandstructure
Peter Blaha
pblaha at theochem.tuwien.ac.at
Wed Dec 23 13:57:40 CET 2015
a) As expected, something is wrong with your structure.
It should be a hexagonal lattice (H and not P) and the angle gamma
should be 120 and not 60, and also the positions need to be changed then.
With an "H" lattice, wien2k keeps the symmetry properly and is less
affected by rounding errors.
b) And secondly, you did not answer, how you got the "gap" (from
scf-file, output1 or bandstructure or DOS ???)
Forget DOS (there is a smearing parameter set by default !)
when you use a H lattice and meshes which can be divided by 3 (because K
has 1/3,1/3,0 coordinates and only with a mesh like 3 3 1, 6 6 1, 9 9
1, ... the "K"-point is in the mesh), you can use :GAP from scf,
otherwise NOT. (best is to use a mesh conpatible with 2 and 3, so 6,6,1
or 12,12,1 ..., because this includes also the M point.
On 12/23/2015 01:22 PM, Islam, Md F wrote:
> 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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--
P.Blaha
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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
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