Where does the discontinuity of the applied electric sawtooth potential occur in the super cell?|
- Date: 2017/06/26 18:14
- Name: Xiangyang Peng
- Dear OpenMX Developers and Users,
I read the manual of openmx 3.8 about the application of a uniform external electric field given by a sawtooth waveform. I quote the part about the discontinuities of the sawtooth potential as follows:
“If the uniform external electric field is applied to a periodic bulk system without vacuum region, discontinuities of the potential are introduced, which may cause numerical instability. On the other hand, for molecular systems, the discontinuities are located in the vacuum region, indicating that numerical instability may not be induced.”
I am studying the effect of electric field on the heterostructure of graphene and BN. The two layers are separated by about 3.3 angstroms. The supercell I choose is 20 angstroms long along the z axis. The graphene and BN layers are parallel to the xy plane. The vacuum is larger than 16 angstroms along the z axis. I do not want the sawtooth potential discontinuity to occur between the graphene/BN heterostructure.
I would like to ask where I should place the graphene and BN layers so that the discontinuity of the sawtooth potential is located in the vacuum. Should I place both graphene and BN layers above the xy plane (z>0), or should I place the xy plane between the graphene/BN heterstructure (i.e. one layer above the xy plane (z>0) and the other layer below the xy plane (z<0) )?
Thank you very much for your help.