calculate band structure of a two probe system

[zgd1222]

 Hello!
 

 i don't know how to  calculate the band structure of a two probe system using ATK 2008.10 or VNL, Please help me . i will appreciate your help.

[Anders Blom]

A two-probe system does not have periodic boundary conditions (at least note in the transport direction), so a band structure calculation for such a system isn't really possible. But maybe that's not exactly what you want to do...?

[zgd1222]

hi,Wizard,
    thank you for your reply. indead ,i havn't seen anything about the band structure reference of two probe system in ATK or VNL. but i have seen  band structure figures in some papers, such as band figures about one molecule adsorbed on graphene .by the figure ,to see how the molecule affect the electronic properties of graphene.   I don't know if they do this by equivalent bulk  two probe system? please give me a  hint,thank you.
 

[zh]

"one molecule adsorbed on graphene"
For such system, it is usually modeled by a slab model that consists of one layer of graphene, a molecule, and a thick vacuum.  It is not modeled by a two-probe system or its equivalent bulk system. Usually, the authors should roughly but clearly describe the model used in their calculations. The slab model can be described in a periodic supercell.  You may use the VNL to a supercell of graphene sheet, and then put a molecule into this supercell.  The band structure of such periodic system can be done as usual.

[zgd1222]

hello zh
   thank you for your reply and your suggestion. when set up the configuration of molecule adsorbate graphene, i did do what you said.but i want to know the conductance of this system,so  i  change it  into two probe system. do you mean that  i can calculate the band structure using the original configuration not the two probe one, and not affecting the calculation result? please give me a hint, thank you very much.

[zh]

do you mean that  i can calculate the band structure using the original configuration not the two probe one, and not affecting the calculation result? please give me a hint, thank you very much.

Yes, you can do the band structure calculation using the "so-called" original configuration. From the band structure of this  "so-called" original configuration, you can get some useful information about the effect of molecule adsorbate on the electronic structure graphene. For example, as you know, for pure graphene sheet the Fermi level toughs the Dirac point. When the molecule adsorbs on graphene, the position of Fermi level of such system will be shifted due to electron or hole dpoing (i.e, electron transfer).  From this point, you can easily expect the behavior of molecule adsorbate on graphene, i.e., n-type or p-type doping,  you can also imagine the conductivity of such system before doing any practical transport  calculations of a two-probe system.  The following paper may be helpful to you:
PHYSICAL REVIEW B 77, 125416 (2008)
Adsorption of  H2O, NH3, CO, NO2, and NO on graphene: A first-principles study
http://prb.aps.org/abstract/PRB/v77/i12/e125416