Hi, I am trying to calculate the conductance through coupled quantum nanowires. I have basically considered a square lattice with hopping tx in x direction and modulating the coupling between the wires through ty i.e. the hopping in y direction. My system requires periodic boundary condition along x direction and open boundary condition in y direction. Can you please help me in how this can be done using kwant to meet the above boundary conditions. I have mentioned my code below. Since I am new to Kwant, it would be of much help to me if you help me solving this. Regards Deepti Rana def make_sys1(a=1,W=4,barrierpos=1): def onsite_normal(site,p): return( (2 * (p.tx+p.ty) - p.mu) * pauli.s0sz+p.Ez*pauli.szs0)) def onsite_sc(site,p): return (2 * (p.tx+p.ty ) * pauli.s0sz+p.Ez*pauli.szs0)+p.delta*pauli.s0sx) def onsite_barrier(site,p): return((2*(p.tx+p.ty)+ p.Vbarrier-p.mu)*pauli.s0sz+p.Ez*pauli.szs0)) def hopx(site1, site2, p): return -p.tx * pauli.s0sz +1j* p.alphax * pauli.sysz def hopy(site1, site2, p): return -p.ty * pauli.s0sz -1j * p.alphay * pauli.sxsz lat = kwant.lattice.square(a,norbs=4) syst = kwant.Builder() syst[(lat(x, y) for x in range(barrierpos) for y in range(W))]=onsite_barrier syst[kwant.builder.HoppingKind((1, 0), lat, lat)] = hopx syst[kwant.builder.HoppingKind((0, 1), lat, lat)] = hopy sym_left = kwant.TranslationalSymmetry((-a, 0)) lead0 = kwant.Builder(sym_left, conservation_law=-pauli.s0sz) lead0[(lat(0, j) for j in range(W))]=onsite_normal lead0[kwant.builder.HoppingKind((1, 0), lat, lat)] = hopx lead0[kwant.builder.HoppingKind((0, 1), lat, lat)] = hopy sym_right = kwant.TranslationalSymmetry((a, 0)) lead1 = kwant.Builder(sym_right) lead1[(lat(0, j) for j in range(W))]=onsite_sc lead1[kwant.builder.HoppingKind((1, 0), lat, lat)] = hopx lead1[kwant.builder.HoppingKind((0, 1), lat, lat)] = hopy syst.attach_lead(lead0) syst.attach_lead(lead1) syst = syst.finalized() return syst