Gap in pristine graphene DOS

Message

Lian · #1 Post by **Lian** » Tue Jan 14, 2014 7:24 pm

Dear VASP users.

I'm performing density of states calculations on pristine graphene unit cell, using the tetrahedron method (ISMEAR = -5).
I followed the usual procedure for this purpose.
1?) ionic relaxation
2?) SCF charge density calculation
3?) non-SCF DOS calculation with denser k-mesh

The whole DOS seems to be properly reproduced (compared to the literature).
Unfortunately, I always observed a little gap (from 0.2 to 0.4 eV) at the Fermi level whereas pristine graphene is known to be gapless. I increased the k-mesh grid until maximum accepted in VASP (45x45x1) but even the little gap is still present.

Why does this fact occur? Did I miss an important parameter that should be taken into account?

Thanks for your help.

Lian

Lian · #2 Post by **Lian** » Thu Jan 16, 2014 4:41 pm

Hi

No people could help?

Lian · #3 Post by **Lian** » Thu Jan 23, 2014 4:46 pm

Dear people.

I heard from someone that a bad sampling of the reciprocal space could lead to the aforementioned issue.
In principle I should sample so that one k-point fits the high-symmetry K-point of the graphene Brillouin zone.

Now I want to know if it is possible to avoid the use of symmetry in reciprocal space; make a vasp calculation with the entire Brillouin zone instead of the irreducible zone.

Thansk for help.