[Wien] no effect of an external electric field on the splitting in graphene

[Martin Gmitra]

Thank you for your answer. We prepared symmetry of the system
in the same way as you are proposing. All the calculations have
been performed using the following potential expansion in case.in2c:

TOT             (TOT,FOR,QTL,EFG,FERMI)
      -9.0       8.0 0.50 0.05                EMIN, NE, ESEPERMIN, ESEPER0
TETRA    0.000          (GAUSS,ROOT,TEMP,TETRA,ALL      eval)
  0 0  1 0  2 0  3 0  3 3  4 0  4 3  5 0  5 3  6 0  6 3  6 6
 20.00          GMAX
**
I think that the local symmetry we have used is OK. What do you think?
Best,
Martin Gmitra



Most likely this is a "symmetry" problem.

One cannot put the graphene sheet at an arbitrary z-position. Remember,
adding an E-field means that we change the Coulomb-potential.
In order to keep periodicity, we use a zig-zag potential and of course
it does NOT make sense to put an atom at the position of the "kink"
(z=0 or 0.5).

Of course when one adds an E-field along the z-direction, the mirror
symmetry within the graphene plane has gone. Thus it is essential to
have this fact reflected in the local symmetry (eg. you need a LM=1 0
term for the E-field, which is normally absent for a single sheet).

I'd recommend to setup the struct file with 2 graphene layers (at z=0
and 0.25), but one should contain eg. B atoms instead of C. After
symmetry detection, remove the B-sheet (at z=0).

Martin Gmitra schrieb:
>* Dear Wien2k users,
*>*
*>* We are running Wien2k 08.2 version on IBM AIX v 5.3 system (Uni Leoben).
*>* We are interested in effects of an external
*>* electric field on splitting in the graphene. We have recovered 24 micro
*>* eV splitting due to intrinsic spin-orbit interaction
*>* in the K-point. Setting up a ramp potential of rather huge amplitudes
*>* (1000 Ry/20A) has no effect on the splitting at all.
*>* I have not found relevant discussion in mailing list. Therefore, I would
*>* like to share my problem with you.
*>*
*>* The graphene sheet has been placed (i) in the quarter of the unit cell
*>* width (z=0.25) and complex calculations have
*>* run and; (ii) the sheet has been positioned in the origin (z=0) and real
*>* calculations have run with modified ramp
*>* potential in eramps.f within lapw0. The results we have obtained are
*>* almost the same - no change in the splitting.
*>*
*>* My question is:
*>* Is the present implementation of the external electric field suitable
*>* for monoatomic slab structures including
*>* spin-orbit coupling interaction?
*>*
*>* Many thanks,
*>* Martin Gmitra*
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