Hello All, I am trying to calculate the band structure of my system in the presence of an external electric field. From what I understand, I need to add the electric field as a potential in the onsite energy for the Hamiltonian. Now when I calculate the band structure, I have to use kwant.plotter.bands(sys.leads[0]) to avoid the code throwing up an error. Whereas what I want to be plotting is kwant.plotter.bands(sys), i.e. the band structure of the system and not the leads. The latter method gives an error (code pasted below) of the following kind. TypeError: Expecting an instance of InfiniteSystem. I have also gone through the answer at https://mailman-mail5.webfaction.com/pipermail/kwant-discuss/2016-June/00090... . That code by Anton changes the band structure for different values of electric fields (which is what one would expect), whereas the band structure of sys.leads[0] (in my code) does not change at all even on significantly changing the field. I have a few questions if someone can help me with them. 1) What is the difference between plotting a band structure for sys and sys.leads[0]? 2) How can I plot the band structure of my system (and not its leads) from the code below? Where am I going wrong? How do I avoid the error? *import kwant* *a = 2.46* *lat = kwant.lattice.honeycomb(a = a)* *p, q = lat.sublattices* *def hopping(sitei, sitej):* * return -2.8* *def onsite(site):* * x, y = site.pos* * return -0 + 1*(y)* *def central_region(pos):* * x, y = pos* * return abs(x) < 5*a + 1e-8 and abs(y) < 5*a + 1e-8* *sys = kwant.Builder()* *sys[lat.shape(central_region, (0, 0))] = onsite* *sys[lat.neighbors()] = hopping* *sym = kwant.TranslationalSymmetry((-a, 0))* *lead = kwant.Builder(sym)* *lead[lat.shape(lambda s: abs(s[1]) < 5*a + 1e-8, (0, 0))] = 0* *lead[lat.neighbors()] = hopping* *sys.attach_lead(lead)* *sys.attach_lead(lead.reversed())* *kwant.plotter.bands(sys.finalized().leads[1]) # This works fine* *#kwant.plotter.bands(sys.finalized()) # This throws up an error* Any help would be greatly appreciated! Shivang Agarwal