Dear Sir, I am using kwant in windows with the help of notepad++. when I run the following program import matplotlib from matplotlib import pyplot from mpl_toolkits import mplot3d import numpy as np from wraparound import wraparound import kwant
def momentum_to_lattice(k): B = np.array(graphene.prim_vecs).T A = B.dot(np.linalg.inv(B.T.dot(B))) return np.linalg.solve(A, k) def dispersion_2D(syst, args=None, lim=1.5*np.pi, num_points=200): """A simple plot of 2D band structure.""" if args is None: args = [] momenta = np.linspace(-lim, lim, num_points) energies = [] for kx in momenta: for ky in momenta: lattice_k = momentum_to_lattice([kx, ky]) h = syst.hamiltonian_submatrix(args=(list(args) + list(lattice_k))) energies.append(np.linalg.eigvalsh(h)) energies = np.array(energies).reshape(num_points, num_points, -1) emin, emax = np.min(energies), np.max(energies) kx, ky = np.meshgrid(momenta, momenta) fig = pyplot.figure() axes = fig.add_subplot(1, 1, 1, projection='3d') for band in range(energies.shape[-1]): axes.plot_surface(kx, ky, energies[:, :, band], cstride=2, rstride=2, cmap=matplotlib.cm.RdBu_r, vmin=emin, vmax=emax, linewidth=0.1) graphene = 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 = graphene.sublattices bulk_graphene = kwant.Builder(kwant.TranslationalSymmetry(*graphene.prim_vecs)) bulk_graphene[graphene.shape((lambda pos: True), (0, 0))] = 0 bulk_graphene[graphene.neighbors(1)] = 1 dispersion_2D(wraparound(bulk_graphene).finalized()) zigzag_ribbon = kwant.Builder(kwant.TranslationalSymmetry([1, 0])) zigzag_ribbon[graphene.shape((lambda pos: abs(pos[1]) < 9), (0, 0))] = 0 zigzag_ribbon[graphene.neighbors(1)] = 1 kwant.plotter.bands(zigzag_ribbon.finalized()) armchair_ribbon = kwant.Builder(kwant.TranslationalSymmetry([0, np.sqrt(3)])) armchair_ribbon[graphene.shape((lambda pos: abs(pos[0]) < 9), (0, 0))] = 0 armchair_ribbon[graphene.neighbors(1)] = 1 kwant.plotter.bands(armchair_ribbon.finalized(), fig_size=(12, 8)) zigzag_ribbon = kwant.Builder(kwant.TranslationalSymmetry([1, 0])) zigzag_ribbon[a.shape((lambda pos: abs(pos[1]) < 9), (0, 0))] = 0.2 zigzag_ribbon[b.shape((lambda pos: abs(pos[1]) < 9), (0, 0))] = -0.2 zigzag_ribbon[graphene.neighbors(1)] = 1 kwant.plotter.bands(zigzag_ribbon.finalized(), fig_size=(12, 8)) The following error message appeared.. File "C:\Users\Shyam Lochan Bora\Desktop\new 1.py", line 5, in <module> from wraparound import wraparound ModuleNotFoundError: No module named 'wraparound' Help me in this regard