Can any one help explain why fermi reference point in density of state plot for graphene is shifted awy from zero reference point. Calculation is done using Quantum Espresso.
I'm not exactly sure what you mean. The Fermi energy is relative to an undefined background constant (a constant added to the Kohn-Sham or total potential) so can be given any value one pleases. In many codes it will be relative to the 'raw' energy coming from V_Pseudopotential + V_Ha + V_xc
Alternately, if the Fermi energy is not centered at the tip of the two cones it suggests that something is a bit wrong. Probably numerical noise from a too small energy cutoff or an insufficient number of k-points. Try it with 10x10x1 k points and an energy cutoff of at least 500eV
Thank you for your wonderful contribution. I have done the calculations with 14 x 14 x 1 k-pint mesh and as you rightly said the K.E cut-off was set at 500 eV. I think the adjustment in the computation should come from the printed fermi energy value at the end of the scf or nscf calculation. Thank you
Make sure the special points are included in you kpoint mesh. Especially the K point should be there. Depending on the definitition in you programm a gamma centered 3nx3nx1 with n integer should work.
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