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Where does the discontinuity of the applied electric sawtooth potential occur in the super cell? Date: 2017/06/26 18:14 Name: Xiangyang Peng   <xiangyang_peng@xtu.edu.cn> 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. Best regards Xiangyang Peng

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Re: Where does the discontinuity of the applied electric sawtooth potential occur in the super cell? ( No.1 ) Date: 2017/06/27 14:52 Name: T. Ozaki Hi, OpenMX automatically analyzes the geometrical structure you give, and try to place the discontinuity in the middle of vacuum. So, you do not need to worry about the absolute position of the structure. Using v0.cube and v1.cuve files, you can confirm where the discontinuity is placed. Regards, TO Re: Where does the discontinuity of the applied electric sawtooth potential occur in the super cell? ( No.2 ) Date: 2017/06/29 10:27 Name: Xiangyang Peng  <xiangyang_peng@xtu.edu.cn> Thank you very much for your prompt reply. Best regards Xiangyang Peng Do I need ESM method in OpenMx calculation when applying external electric field for a monolayer ? ( No.3 ) Date: 2018/02/02 10:45 Name: Santu Baidya  <santubaidya2009@gmail.com> I have the related question regarding applying external electric field in Openmx for a monolayer with vacuum along z-direction. Can you please tell me if ESM tags need to be included during applying external electric field. Re: Where does the discontinuity of the applied electric sawtooth potential occur in the super cell? ( No.4 ) Date: 2018/03/02 15:10 Name: T. Ozaki References: t-ozaki@issp.u-tokyo.ac.jp Hi, There are two ways to apply external electric field as explained at http://www.openmx-square.org/openmx_man3.8/node90.html http://www.openmx-square.org/openmx_man3.8/node138.html If the sawtooth electric field is used, ESM tags are irrelevant. Regards, TO

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