While studying 2.3.transport_through_barrier.ipynb, a tutorial in gitlab, I tried to find the transimission by changing the lattice to a graphene nanoribbon rather than a square. Here is the code I tried. import numpy as np import kwant from matplotlib import pyplot lat = kwant.lattice.general([[1, 0], [1/2, np.sqrt(3)/2]], # lattice vectors [[0, 0], [0, 1/np.sqrt(3)]]) # Coordinates of the sites a, b = lat.sublattices def make_lead_x(W=10, t=1): syst = kwant.Builder(kwant.TranslationalSymmetry([-1, 0])) syst[(lat(0, y) for y in range(W))] = 4 * t syst[lat.neighbors()] = -t return syst def make_wire_with_flat_potential(W=10, L=2, t=1): def onsite(s, V): return (4 - V) * t # Construct the scattering region. sr = kwant.Builder() sr[(lat(x, y) for x in range(L) for y in range(W))] = onsite sr[lat.neighbors()] = -t # Build and attach lead from both sides. lead = make_lead_x(W, t) sr.attach_lead(lead) sr.attach_lead(lead.reversed()) return sr def plot_transmission(syst, energy, params): # Compute conductance trans = [] for param in params: smatrix = kwant.smatrix(syst, energy, args=[param]) trans.append(smatrix.transmission(1, 0)) pyplot.plot(params, trans) _syst = make_wire_with_flat_potential() kwant.plot(_syst) _syst = _syst.finalized() kwant.plotter.bands(_syst.leads[0]) plot_transmission(_syst, 1, np.linspace(-2, 0, 51)) Error says 'Polyatomic' object is not callable. I did a search lat = kwant.lattice.general([[1, 0], [1/2, np.sqrt(3)/2]], # lattice vectors [[0, 0], [0, 1/np.sqrt(3)]]) # Coordinates of the sites a, b = lat. sublattices I understand that this code is polyatomic, and it is not correct to apply it to (lat(x, y). But i can't find a solution. Can you help me?