LEPSILON for graphene

Message

giacomo giorgi · #1 Post by **giacomo giorgi** » Mon Apr 15, 2013 10:10 am

Dear All,
using this INCAR (for a the two atom cell of graphene)

SYSTEM = graphene
ENCUT=500.0 eV
ISTART=1
ICHARG=0
ISMEAR = 0
SIGMA = 0.05
LEPSILON=.TRUE.
LRPA=.TRUE.

and progressively increasing the KPOINTS sampling, the change of MACROSCOPIC STATIC DIELECTRIC TENSORS are the following.

>>> (KPOINTS = x x 1)

>>> x=24
>>> 32572.891 -18632.231 0.000
>>> -18632.231 11058.249 0.000
>>> 0.000 0.000 1.285

>>> x=72
>>> 5911.373 -3311.514 0.000
>>> -3311.514 2087.567 0.000
>>> 0.000 0.000 1.284

>>> x=144
>>> 6699.885 -3783.612 0.000
>>> -3783.612 2330.947 0.000
>>> 0.000 0.000 1.284

>>> x=200
>>> 4631.198 -2586.121 0.000
>>> -2586.121 1645.003 0.000
>>> 0.000 0.000 1.544

Are these so large oscillations a "normal" result?
I suspect they are not. Is there anyone able to explain me where I am failing? Am I misunderstanding any relevant concept of physics?

thanks a lot!!
Very best,
Giacomo

giacomo giorgi · #2 Post by **giacomo giorgi** » Thu Apr 18, 2013 7:19 am

ANY IDEA?

giacomo giorgi · #3 Post by **giacomo giorgi** » Tue Apr 23, 2013 11:48 pm

Please help me. None of the people I asked was able to figure out this problem. Can I calculate LEPSILON for graphene?
Thanks!!!

naidu · #4 Post by **naidu** » Mon May 05, 2014 6:04 am

Dear Giacomo,

are you able to find answer to this problem? I am trying to calculated the dielectric properties of Graphene using the LEPSILON tag. But I am not sure whether we can use this method for calculating the dielectric properties of Graphene or not? When I use LEPSILO=T and LPEAD=.T., I am getting the error message "Checking the occupancies, it is not an insulator". Can you share your experience?

Thanks,
Naidu.