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I'm a beginner at DFT calculations with VASP software. I use it to calculate the band structure of graphene and I obtain the following result: enter image description here I used it to calculate the band structure of graphene with the tight binding method by hand. It should not be squeezed on the right hand side of the Dirac cone in the Fermi level as shown in the figure. How can I explain this phenomenon? My question might be very stupid. Is it from the effect of another orbital that I didn't take into account when I use tight binding method?

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    $\begingroup$ @JensenPang Have you looked at Tight binding and DFT band-structures for other materials? Why compare those two? The tight-binding approximation works very well only in the case of narrow bands where you often consider the band edges to adhere well to the parabolic band approximation - Basically, Energy varying as a quadratic function of 'K'. There will definitely be a difference in curvatures between tight-binding and DFT in my opinion. $\endgroup$ – livars98 Jun 7 '20 at 5:08
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Oh! I found the answer already. Since I'm doing the calculation along the High symmetry point. Im doing the calculation along G -> K -> M -> G, that's why the right hand sides show such phenomena. In tight binding I plot the band along G -> K -> G. I try to reproduce the band along this direction, it matched with the tight binding solution. Thanks guys. It's my mistake.

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