Hello everyone,
I have reproduced the DFT tutorial calculation for graphene. At the K point, without including spin–orbit coupling, I obtain a small gap.
The energies of the π and π* bands at the K point are:
π = 0.7479841447 × 10⁻³ Hartree
π* = 0.7481050960 × 10⁻³ Hartree
This corresponds to a small but non-zero gap, whereas graphene is expected to be gapless at the K point in the absence of SOC.
How can this unphysical gap be explained?
Any insights would be appreciated. Thank you.