[Kwant] regarding error message

[shyam lochan bora]

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

[Joseph Weston]

Dear Shyam,

Post by shyam lochan bora
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

'wraparound' is now included with Kwant, as of version 1.3.
You can change the line:

    from wraparound import wraparound

to

    from kwant.wraparound import wraparound

to get wraparound working.

Happy Kwanting,

Joe

[shyam lochan bora]

thank you so much for your help

Post by Joseph Weston
Dear Shyam,

Post by shyam lochan bora
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

'wraparound' is now included with Kwant, as of version 1.3.
from wraparound import wraparound
to
from kwant.wraparound import wraparound
to get wraparound working.
Happy Kwanting,
Joe