Dear Fhokrul<br />
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. <br />
Here is a cif file of graphene based on the graphite structure in which I have simply increase the c parameter. <br />
The structure you are using may explain why you still have a gap (symetry problem). <br />
Best Regards<br />
Xavier<br />
<br />
<br />
#======================================================================<br />
<br />
# CRYSTAL DATA<br />
<br />
#----------------------------------------------------------------------<br />
<br />
data_VESTA_phase_1<br />
<br />
<br />
_pd_phase_name 'C'<br />
_cell_length_a 2.45600<br />
_cell_length_b 2.45600<br />
_cell_length_c 15.00000<br />
_cell_angle_alpha 90<br />
_cell_angle_beta 90<br />
_cell_angle_gamma 120<br />
_symmetry_space_group_name_H-M 'P 63 m c'<br />
_symmetry_Int_Tables_number 186<br />
<br />
loop_<br />
_symmetry_equiv_pos_as_xyz<br />
'x, y, z'<br />
'-y, x-y, z'<br />
'-x+y, -x, z'<br />
'-x, -y, z+1/2'<br />
'y, -x+y, z+1/2'<br />
'x-y, x, z+1/2'<br />
'-y, -x, z'<br />
'-x+y, y, z'<br />
'x, x-y, z'<br />
'y, x, z+1/2'<br />
'x-y, -y, z+1/2'<br />
'-x, -x+y, z+1/2'<br />
<br />
loop_<br />
_atom_site_label<br />
_atom_site_occupancy<br />
_atom_site_fract_x<br />
_atom_site_fract_y<br />
_atom_site_fract_z<br />
_atom_site_adp_type<br />
_atom_site_B_iso_or_equiv<br />
_atom_site_type_symbol<br />
C1 1.0 0.000000 0.000000 0.000000 Biso 1.000000 C<br />
C2 1.0 0.333333 0.666667 0.000000 Biso 1.000000 C<br />
<br />
<br />
<br />
"Islam, Md F" <islamm@uta.edu> a écrit :<br />
<br />
> Sorry, in my earlier email, I meant to say with 30 x 30 x 1 mesh, gap <br />
> is smaller but<br />
> it doesn't close completely.<br />
><br />
> Thanks,<br />
> Fhokrul<br />
><br />
><br />
> ________________________________________<br />
> From: wien-bounces@zeus.theochem.tuwien.ac.at <br />
> [wien-bounces@zeus.theochem.tuwien.ac.at] On Behalf Of Islam, Md F <br />
> [islamm@uta.edu]<br />
> Sent: Wednesday, December 23, 2015 6:22 AM<br />
> To: A Mailing list for WIEN2k users<br />
> Subject: Re: [Wien] Graphene bandstructure<br />
><br />
> Hi Prof Blaha,<br />
><br />
> Here is the structure I am using. I tried to be as precise as <br />
> possible with position coordinates.<br />
> I think size of the vacuum is sufficiently large so that <br />
> supercell-supercell interaction is negligible.<br />
> So far what I have got is that with LDA xc if I use 25 x 25 x 1 <br />
> k-mesh there is a gap at the Fermi<br />
> level (which passes through K point) but if I use 30 x 30 x 1 k-mesh, <br />
> gap closes but DOS is not<br />
> zero at the Fermi level (about 0.001/eV). Please let me know if I am <br />
> doing anything wrong with<br />
> this calculation.<br />
><br />
><br />
> Thanks,<br />
> Fhokrul<br />
><br />
><br />
> Graphene<br />
> P LATTICE,NONEQUIV.ATOMS: 2<br />
> MODE OF CALC=RELA unit=bohr<br />
> 4.647800 4.647800 30.000000 90.000000 90.000000 60.000000<br />
> ATOM -1: X=0.00000000 Y=0.00000000 Z=0.50000000<br />
> MULT= 1 ISPLIT= 8<br />
> C NPT= 781 R0=0.00010000 RMT= 1.3200 Z: 6.0<br />
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<br />
> 0.0000000 1.0000000 0.0000000<br />
> 0.0000000 0.0000000 1.0000000<br />
> ATOM -2: X=0.66666667 Y=0.66666667 Z=0.50000000<br />
> MULT= 1 ISPLIT= 8<br />
> C NPT= 781 R0=0.00010000 RMT= 1.3200 Z: 6.0<br />
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<br />
> 0.0000000 1.0000000 0.0000000<br />
> 0.0000000 0.0000000 1.0000000<br />
> 12 NUMBER OF SYMMETRY OPERATIONS<br />
> -1-1 0 0.00000000<br />
> 0 1 0 0.00000000<br />
> 0 0-1 0.00000000<br />
> 1<br />
> -1-1 0 0.00000000<br />
> 0 1 0 0.00000000<br />
> 0 0 1 0.00000000<br />
> 2<br />
> -1-1 0 0.00000000<br />
> 1 0 0 0.00000000<br />
> 0 0-1 0.00000000<br />
> 3<br />
> -1-1 0 0.00000000<br />
> 1 0 0 0.00000000<br />
> 0 0 1 0.00000000<br />
> 4<br />
> 0 1 0 0.00000000<br />
> -1-1 0 0.00000000<br />
> 0 0-1 0.00000000<br />
> 5<br />
> 0 1 0 0.00000000<br />
> -1-1 0 0.00000000<br />
> 0 0 1 0.00000000<br />
> 6<br />
> 0 1 0 0.00000000<br />
> 1 0 0 0.00000000<br />
> 0 0-1 0.00000000<br />
> 7<br />
> 0 1 0 0.00000000<br />
> 1 0 0 0.00000000<br />
> 0 0 1 0.00000000<br />
> 8<br />
> 1 0 0 0.00000000<br />
> -1-1 0 0.00000000<br />
> 0 0-1 0.00000000<br />
> 9<br />
> 1 0 0 0.00000000<br />
> -1-1 0 0.00000000<br />
> 0 0 1 0.00000000<br />
> 10<br />
> 1 0 0 0.00000000<br />
> 0 1 0 0.00000000<br />
> 0 0-1 0.00000000<br />
> 11<br />
> 1 0 0 0.00000000<br />
> 0 1 0 0.00000000<br />
> 0 0 1 0.00000000<br />
> 12<br />
><br />
><br />
><br />
><br />
> ________________________________________<br />
> From: wien-bounces@zeus.theochem.tuwien.ac.at <br />
> [wien-bounces@zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha <br />
> [pblaha@theochem.tuwien.ac.at]<br />
> Sent: Tuesday, December 22, 2015 3:29 PM<br />
> To: A Mailing list for WIEN2k users<br />
> Subject: Re: [Wien] Graphene bandstructure<br />
><br />
> The two eigenvalues at K must be identical by symmetry.<br />
><br />
> If you have a splitting of some meV it means that your structure is<br />
> slightly wrong.<br />
><br />
> Typical errors: positions of 1/3 and 2/3 must be given in full precision.<br />
> 0.3333 is NOT 1/3<br />
><br />
> Am 22.12.2015 um 20:31 schrieb Islam, Md F:<br />
>> Hi Prof Blaha,<br />
>><br />
>> I have got the gap from plotting bandstructure as well as DOS <br />
>> calculations.<br />
>> I can see the linear dispersion at the K point just like the way it <br />
>> is suppose to be<br />
>> when I plot all the bands in eV range. But if I zoom in at the K <br />
>> point in meV range,<br />
>> I can see the gap.<br />
>><br />
>> I don't think there is anything wrong with the structure. I did <br />
>> check all bond lengths,<br />
>> angles before I ran the calculations and they are correct. I suspect <br />
>> I may have to adjust<br />
>> parameters. I started to see some difference with LDA xc functional <br />
>> with larger k mesh.<br />
>><br />
>><br />
>> Thanks,<br />
>> Fhokrul<br />
>><br />
>><br />
>><br />
>><br />
>> ________________________________________<br />
>> From: wien-bounces@zeus.theochem.tuwien.ac.at <br />
>> [wien-bounces@zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha <br />
>> [pblaha@theochem.tuwien.ac.at]<br />
>> Sent: Tuesday, December 22, 2015 11:35 AM<br />
>> To: A Mailing list for WIEN2k users<br />
>> Subject: Re: [Wien] Graphene bandstructure<br />
>><br />
>> Graphene is metallic by "symmetry", i.e. EF is at a 2-fold eigenvalue at<br />
>> the K-point and bands cross with a linear dispersion.<br />
>><br />
>> From where do you know that graphene has a gap in your calculations ??<br />
>><br />
>> From :gap in the scf file or from plotting the bandstructure or ...<br />
>><br />
>> It the state at K is not degenerate, you have the wrong symmetry and are<br />
>> not doing graphene.<br />
>><br />
>> Am 22.12.2015 um 16:51 schrieb Islam, Md F:<br />
>>> Hi,<br />
>>><br />
>>> I am trying to do a bandstructure calculation of graphene to <br />
>>> check if I can<br />
>>> reproduce results discussed in literature (I am using a unit cell <br />
>>> of 2 atoms).<br />
>>> With spin-orbit coupling, there should be a gap of the order of few <br />
>>> micro-eV<br />
>>> and without spin-orbit, there should not be any gap at Dirac point. <br />
>>> But I am<br />
>>> getting a gap of meV even without spin-orbit. I tried both GGA and LDA with<br />
>>> very dense mesh but the gap does not close. So I am wondering if anyone<br />
>>> have any suggestion about how to do it in Wien2k.<br />
>>><br />
>>><br />
>>> Thanks,<br />
>>> Fhokrul<br />
>>> _______________________________________________<br />
>>> Wien mailing list<br />
>>> Wien@zeus.theochem.tuwien.ac.at<br />
>>> <a target="_blank" href="http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien">http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien</a><br />
>>> SEARCH the MAILING-LIST at: <br />
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>>><br />
>><br />
>> --<br />
>> --------------------------------------------------------------------------<br />
>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br />
>> Phone: +43-1-58801-165300 FAX: +43-1-58801-165982<br />
>> Email: blaha@theochem.tuwien.ac.at WIEN2k: <a target="_blank" href="http://www.wien2k.at">http://www.wien2k.at</a><br />
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>> <a target="_blank" href="http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien">http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien</a><br />
>> SEARCH the MAILING-LIST at: <br />
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>><br />
><br />
> --<br />
> --------------------------------------------------------------------------<br />
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna<br />
> Phone: +43-1-58801-165300 FAX: +43-1-58801-165982<br />
> Email: blaha@theochem.tuwien.ac.at WIEN2k: <a target="_blank" href="http://www.wien2k.at">http://www.wien2k.at</a><br />
> WWW: <a target="_blank" href="http://www.imc.tuwien.ac.at/staff/tc_group_e.php">http://www.imc.tuwien.ac.at/staff/tc_group_e.php</a><br />
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