Re: [Kwant] NNN hopping with periodic BC
Sorry I only just saw this email; please remember to "reply All" so that the email gets sent to the mailing list too! > Thanks. But except the PBC imposed on transverse direction, I need > attach the lead on longitude direction. So I want the transverse size > of sample to be finite. > Ah I see. In this case your could consider using 'kwant.wraparound' [1]. In your case you would want to set the 'keep' paramter to '0' to keep the 0th translational symmetry in the wrapped around system. Using wraparound in this way will produce a Builder with a single (longitudinal) translational symmetry that you may use as a lead. The produced Builder will have an (additional) parameter 'k_y'; the transverse momentum. Don't be confused by the name; it will also work when the "wrapped" symmetry vector was not in the "y" direction! There were already several people on the mailing list who used wraparound, so you could also search the archives. If it's still not clear after this post back to this thread. Happy Kwanting, Joe [1]: https://kwant-project.org/doc/1/reference/generated/kwant.wraparound.wraparound#kwant.wraparound.wraparound
Re: [Kwant] NNN hopping with periodic BC
Hi, > I want to create a graphene-like system with periodic BC at transverse > direction. I’m following > > the discussion at > https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00036.html. > > > If you only want 1 direction to have periodic boundary conditions (and finite in the other direction) why not just create a system with a 1D translational symmetry? This will make your life a lot easier. Happy Kwanting, Joe
[Kwant] NNN hopping with periodic BC
Hello, I want to create a graphene-like system with periodic BC at transverse direction. I'm following the discussion at https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00036.html. For nearest-neighbor hopping, it works. There is hopping between the upper and lower side. But when I add NNN hopping using: A,B=graphene.sublattices sys[A.neighbors()]=hopp_qsvh sys[B.neighbors()]=hopp_qsvh The NNN hopping doesn't exist between the upper and lower side. Is there any way to solve it? Thank you, Yuhao Attached is the code: import numpy as np import kwant X,Y = 4, 4 s0=np.identity(2) sz=np.array([[1,0],[0,-1]]) graphene = kwant.lattice.honeycomb(1,'b') A,B=graphene.sublattices def rectangle(pos): x, y = pos return -X/2 < x < X/2 def onsite_qsvh(site): x,y=site.pos if y<0: onsite_a = .4*s0 onsite_b = -.4*s0 return onsite_a if site.family == A else onsite_b else: return np.zeros([2,2]) def hopp_qsvh(site1,site2): x1,y1=site1.pos x2,y2=site2.pos hop_a = .4*1j*sz hop_b = -.4*1j*sz if (y1+0.1)*(y2+0.1)>0 and y1+0.1>0: return hop_a if site1.family == A else hop_b else: return np.zeros([2,2]) sym = kwant.TranslationalSymmetry(graphene.vec((-Y/2,Y))) anc = kwant.Builder(sym) anc[graphene.shape(rectangle,(0, 0))] = None anc[graphene.neighbors()] = None sys = kwant.Builder() sys[anc.sites()] = onsite_qsvh sys[((a, sym.to_fd(b)) for a, b in anc.hoppings())] = -s0 sys[A.neighbors()]=hopp_qsvh sys[B.neighbors()]=hopp_qsvh sys = sys.finalized() kwant.plot(sys,fig_size=(20, 10))
