QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: dwh on November 21, 2012, 12:07

Title: bandstructure
Post by: dwh on November 21, 2012, 12:07

Hello everyone. I come to two problems when I calculate the bandstructure of graphene.
The first one. The bandstructure of graphene is different from the others result that had published(PHYSICAL REVIEW B 77, 035427
2008 ),expecially the band above the Fermi Level,and I try the four kinds of Exchange correction including LDA.PZ, LSDA.PZ, GGA.PBE and SGGA.PBE, but the result is still different from the published one .How can I get the fully same result comparing with the published?
The second one. The bandstructure of supercell graphene is different from the unit cell graphene. I consider that they should be the same because I consider the first Brillouin zone. Could you describe its reasion in detail? thanks

Title: Re: bandstructure
Post by: zh on November 21, 2012, 12:27

First of all, it is well-known that the ground state of graphene is  non-magnetic. so it is meaningless to do the spin-polarized calculations (e.g., LSDA, SGGA), because they will give  the exact results of non-spin-polarized calculations.

Second, graphene is zero-gap, so a quite dense k-mesh for the k-point sampling in the self-consistent  calculations is needed. The 9x9 k-mesh may be not sufficient.

When a supercell is used, the obtained band structure is not easy to compare with the one obtained by the primitive unit cell, because the band folding.

The difference between your results and the published one mainly exists for the sigma bands. You may check the lattice constant of graphene and the C-C bond length in your calculations and those  used in the published paper. Are they same?

Title: Re: bandstructure
Post by: dwh on November 21, 2012, 14:49

I reset the parameter that is the same with the published paper for calculating the graphene bandstructure ,and the result is still different from the published one and it is same for my result before.

Title: Re: bandstructure
Post by: kstokbro on November 25, 2012, 00:17

see:
http://quantumwise.com/forum/index.php?topic=2021.msg9772;topicseen#msg9772

Title: Re: bandstructure
Post by: Roy on November 26, 2012, 12:35

Hello Everyone,

I want to plot an energy band diagram of graphene using matlab and to compare the result with ATK result. Can anyone  please help me with the Matlab script for Energy band diagram of graphene using Hamiltonian.

Thank You.

Title: Re: bandstructure
Post by: kstokbro on November 26, 2012, 15:00

If you select a bandstructure object in VNL you can save it as ascii data, which you can read into matlab.

Title: Re: bandstructure
Post by: Shatendra on November 29, 2012, 10:44

The scripts given in Forum are not working. Can some one elaborate how to calculate the bandstructure from .nc file?

Title: Re: bandstructure
Post by: kstokbro on November 29, 2012, 11:33

To calculate the bandstructure from a converged calculation see:
http://www.quantumwise.com/publications/tutorials/mini-tutorials/166-computing-quantities-from-converged-calculations

Please let us know which script on the forum, (post and name), which is not working and the error message you get.

Title: Re: bandstructure
Post by: Chinha on November 30, 2012, 14:18

As graphene is known as a zero gap material, and in armchair graphene it shows a bit bandgap. Now using hamiltonian (tight binding) i am able to produce the bandstructure of graphene in matlab.I want to know if there is a possible way to get the bandstructure of graphene (not a gnr) using matalb....ascii format as replied to roy's question is not working for me....
Thanks in advance.