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

[Martin Gmitra]

Dear Wien2k users,
To move ahead I checked lapw0.F and xcpot3.F for corresponding parts
including ramp potential to xc potential. There are some commented parts
of the code. However, I am not expert, I would like to ask you if you can
check whether some relevant parts should not be uncommented for proper
including the ramp potential in lapw0. I am referring to Wien2k version 08.2
and 08.3.
Many thanks,
Martin Gmitra


On Tue, Sep 9, 2008 at 11:06 AM, Martin Gmitra <
martin.gmitra at physik.uni-regensburg.de> wrote:

> 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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