Dear Kwant Developers, I am trying to calculate the conductance of a 3D system with dimension L × W × H, by imposing periodic boundary conditions in all three directions. I am able to calculate the band structure but unable to calculate the corresponding conductance using kwant.smatrix. I am not sure whether kwant is able to do transport calculations on systems with periodic boundaries using smatrix. Please advise. The code is following import kwant import scipy.sparse.linalg as sla import matplotlib.pyplot as plt import tinyarray import numpy as np from numpy import cos, sin, pi import cmath from cmath import exp from matplotlib import rc, rcParams rc('text', usetex=True) rc('axes', linewidth=2) rc('font', weight='bold') #rcParams['text.latex.preamble'] = [r'\usepackage{sfmath} \boldmath'] #rcParams['text.latex.preamble'] = [r'\usepackage{sfmath} \boldmath'] sigma_0 = tinyarray.array([[1, 0], [0, 1]]) sigma_x = tinyarray.array([[0, 1], [1, 0]]) sigma_y = tinyarray.array([[0, -1j], [1j, 0]]) sigma_z = tinyarray.array([[1, 0], [0, -1]]) def make_sys(a=1, m_0 = 2, L=1, W=100, H=1, t=1.0, t_z=0.0, phi=0.01): #L=10; W=80; H=60; def onsite(site): return 2 * m_0 * sigma_x def hoppingx(site0, site1): y = site1.pos[1] return (t * sigma_x) def hoppingy(site0, site1): return -1j * t * sigma_y - (m_0/2) * sigma_x def hoppingz(site0, site1): y = site1.pos[1] return (-1j * t * sigma_z - (m_0/2) * sigma_x - 1j * t_z * sigma_0) * exp(2 * pi * 1j * (y) * phi) lat =kwant.lattice.cubic(norbs=2) #sys = kwant.Builder(kwant.TranslationalSymmetry(lat.vec((0, 0, H)))) #sys[(lat(x, y, z) for x in range(L) for y in range(W) for z in range(H))] = onsite #sys = kwant.Builder(kwant.TranslationalSymmetry((L, 0, 0),(0, 0, H))) #sys[(lat(0, y, 0) for y in range(W))] = onsite sys = kwant.Builder(kwant.TranslationalSymmetry((L, 0, 0),(0, W, 0),(0, 0, H))) sys[lat.shape(lambda p: True, (0,0,0))] = onsite sys[kwant.builder.HoppingKind((1, 0, 0), lat, lat)] = hoppingx sys[kwant.builder.HoppingKind((0, 1, 0), lat, lat)] = hoppingy sys[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = hoppingz sys = kwant.wraparound.wraparound(sys, keep=None) leadL = kwant.Builder(kwant.TranslationalSymmetry((-a, 0, 0),lat.vec((0, W, 0)),lat.vec((0, 0, H)))) leadL[(lat(0, y, z) for y in range(W) for z in range(H))] = onsite leadL[kwant.builder.HoppingKind((1, 0, 0), lat, lat)] = hoppingx leadL[kwant.builder.HoppingKind((0, 1, 0), lat, lat)] = hoppingy leadL[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = hoppingz leadR = kwant.Builder(kwant.TranslationalSymmetry((a, 0, 0),lat.vec((0, W, 0)),lat.vec((0, 0, H)))) leadR[(lat(0, y, z) for y in range(W) for z in range(H))] = onsite leadR[kwant.builder.HoppingKind((1, 0, 0), lat, lat)] = hoppingx leadR[kwant.builder.HoppingKind((0, 1, 0), lat, lat)] = hoppingy leadR[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = hoppingz leadL = kwant.wraparound.wraparound(leadL, keep=0) leadR = kwant.wraparound.wraparound(leadR, keep=0) sys.attach_lead(leadL) sys.attach_lead(leadR) sys = sys.finalized() return sys syst=make_sys() def plot_bands_2d(syst, momenta=(101, 101, 101), ky=0, kz=0): if not isinstance(syst, kwant.system.FiniteSystem): raise TypeError("Need a system without symmetries.") fig = plt.figure(figsize=(5, 5)) #kwant.plotter.bands(syst.leads[0], momenta=np.linspace(-np.pi, np.pi, 101), show=False) kxs = np.linspace(-np.pi, np.pi, momenta[0]) def get_energies(ky=ky, kz=kz): energies = [np.linalg.eigvalsh(syst.hamiltonian_submatrix ((kx, ky, kz))) for kx in kxs] return energies energies = np.array(get_energies(ky=ky, kz=kz)) # Plot the band structure for band in np.array(energies).T: plt.plot(kxs, band) plt.ylim(-2.5, 2.5) plt.xlim(-pi, pi) plt.xlabel("kx") plt.ylabel("Energy") plot_bands_2d(syst) kzs = np.linspace(-pi,pi,101) kys = np.linspace(-pi,pi,101) energies = np.linspace(0.0, 0.5, 30) data=[] for energy in energies: Tkx = np.zeros(101) for i in np.arange(len(kzs)): kz=kzs[i] ky=kys[i] smatrix = kwant.smatrix(syst, energy, [kz], [ky]) Tkx[i]=smatrix.transmission(1, 0) data.append(sum(Tkx)) plt.plot(energies, data) plt.show() Also as a separate question, I am trying to run the notebook Kubo_Bastin_conductivity_with_periodic_boundary_conditions.ipynb from https://gitlab.com/kpm-tools/bloch/-/tree/master/examples?ref_type=heads to understand the kubo conductivity calcualton on a system with periodic boundaries but various errors are there in importing bloch.py. I am using kwant.__version__ = '1.4.4'. Please help in this regard. Thanks in advance. -- Best Regards, Naveen Yadav Department of Physics & Astrophysics University Of Delhi New Delhi-110007