My Community

Hi,
I am just doing a small test for graphene and I still don't understand why the lattice parameter is always calculated to be around 1.23A while it should be around 1.42.
SYSTEM = Graphene
ISTART=0
ISPIN=1
POTIM=.1
ENCUT = 500
NSW =100
LREAL=.FALSE.
LWAVE=.TRUE.
LCHARG=.TRUE.
IBRION=1
ISIF=2
LORBIT=10
ISMEAR=0
NPAR = 12

Graphene
1.00000000000000
1.2300000000000000 -2.1300000000000000 0.0000000000000000
1.2300000000000000 2.1300000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 20.0000000000000000
C
2
Cartesian
0.0000000000000000 0.0000000000000000 0.0000000000000000
1.4200000000000000 0.0000000000000000 0.0000000000000000

10x10x10
0
Gamma
10 10 1
0. 0. 0.

I tried different settings.....but still giving the same relaxed structure!
Many thanks,
Tahar

Are you sure that your lattice vectors were set properly? Your cell is 1.23A long in x-axis and you want to separate your atoms by more than that, maybe that is the reason? But this is only my quess, so it may be wrong.

Firstly, I think your initial poscar is far away from graphene.
I just visualized it using VMD, I couldn't see any hexagonal structure as graphene.
Secondly, have a look at the link below for the INCAR tags about relaxation!
Good Luck!