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

[Peter Blaha]

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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