Dear Sir,
I am a PhD student of Hong Kong University of Science and Technology. I
want to use KWANT to caculate Hall resistance of a Hall bar structure.We
can get the conductance between 6 electrodes, but how to get hall
resistance? Can you give me some help? Thank you very much.
Best Regards,
Zhang Bing

Dear all,
I want to calculate the conductance and the band structure of a bulk
graphene system.(infinite in y direction) I have checked the source code
for the calculation of band structure.
https://github.com/kwantproject/kwant/blob/7c55b0cb2d0dec163e5483dea8ffdbc8…
It seems that we can get the sys.cell_hamiltonian and hopping between the
sys.cell_hamiltonian in kwant. In y direction, we can also have
sys.cell_hamiltonian and hopping, then it can be extended to infinite in y
direction: V^\dagger e^{iky} + H + Ve^{-iky}. I am not familiar with kwant
coding. Can anyone help me to write some code lines to do these
calculations? Or you can also change the Tutorial 2.2.3 as an example.
Thanks in advance!
Best wishes
Weiyuan Tong

Dear Kwant community,
Is there a particular reason why kwant is configured to work with sequential MUMPS instead of parallel? I am working with very large systems (~10^8 sites) on a well equipped computer cluster, and was wondering if I could easily extend MUMPS support to parallel instead of just sequential?
Best regards, Abdul

Hello,
I am trying to plot spin-up and spin-down LDOS in quantum Hall, but always
got the following error message:
Traceback (most recent call last):
File "C:\Python34\codes\qhe.py", line 129, in <module>
kwant.plotter.map(sys, d)
File "C:\Python34\lib\site-packages\kwant\plotter.py", line 1547, in map
img, min, max = mask_interpolate(coords, value, a, method, oversampling)
File "C:\Python34\lib\site-packages\kwant\plotter.py", line 1441, in
mask_interpolate
raise ValueError("The number of sites doesn't match the number of"
ValueError: The number of sites doesn't match the number ofprovided values.
I tried to following the solution offered by Anton and Michael here (
https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00006.html)
by reshaping the array like this
*def density_lead0(sys, energy, args):*
* wf = kwant.wave_function(sys, energy, args)*
* prob = (abs(wf(0))**2)*
* return np.sum(prob.reshape(-1,2), axis=1)*
unfortunately, I always got similar error message. Any advice will be
greatly appreciated.
Best regards,
Fauzi
PS. This is the full code:
import math
from cmath import exp
import numpy
import numpy as np
from matplotlib import pyplot
import kwant
from kwant.digest import gauss
# For matrix support
import tinyarray
# Pauli matrices
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]])
#define hopping energy
t = 1
#Zeeman energy
e_z = 0.015
#peierls substitution
def hopping(sitei, sitej, phi, salt):
xi, yi = sitei.pos
xj, yj = sitej.pos
return -t * exp(-0.5j * phi * (xi - xj) * (yi + yj)) * sigma_0
def onsite(site, phi, salt):
return 0.05 * gauss(repr(site), salt)*sigma_0 + 4 * t *sigma_0 +
e_z*sigma_z
def make_system(L=40):
def central_region(pos):
x, y = pos
return -L < x < L and \
abs(y) < L - 27.5 * math.exp(-x**2 / 20**2)
lat = kwant.lattice.square()
sys = kwant.Builder()
sys[lat.shape(central_region, (0, 0))] = onsite
sys[lat.neighbors()] = hopping
sym = kwant.TranslationalSymmetry((-1, 0))
lead = kwant.Builder(sym)
lead[(lat(0, y) for y in range(-L + 1, L))] = 4 * t *sigma_0 +
e_z*sigma_z #disorder-free
lead[lat.neighbors()] = hopping
sys.attach_lead(lead)
sys.attach_lead(lead.reversed())
return sys.finalized()
sys = make_system()
energy = 0.10
#kwant.plot(sys)
# Calculate and plot QHE conductance plateaus.
reciprocal_phis = numpy.linspace(4, 60, 150)
conductances = []
for phi in 1 / reciprocal_phis:
smatrix = kwant.smatrix(sys, energy, args=[phi, ""])
conductances.append(smatrix.transmission(1, 0))
pyplot.plot(reciprocal_phis, conductances)
pyplot.show()
# Calculate and plot a QHE edge state.
def density_lead0(sys, energy, args):
wf = kwant.wave_function(sys, energy, args)
prob = (abs(wf(0))**2)
return np.sum(prob.reshape(-1,2), axis=1)
def density_lead1(sys, energy, args):
wf = kwant.wave_function(sys, energy, args)
prob = (abs(wf(1))**2)
return np.sum(prob.reshape(-1,2), axis=1)
d = density_lead0(sys, energy, [1/40.0, ""]) + density_lead1(sys, energy,
[1/40.0, ""])
kwant.plotter.map(sys, d)

Dear All,
I am currently planning to work on stanene (2D tin), it is a quantum spin Hall insulator and other topological insulator. Majority of the work in this field is done by using VASP and other DFT code based tools. I would like to know if one can build topological insulators and 2D materials other than graphene (like stanene) in KWANT and compute it's electronic properties, such as edges states, chiral current etc. If yes can you can direct me to a resource or reference.
Thank You,Ghadiyali Mohammed Kader,Research Scholar,Physics Dept.University of Mumbai.

Hello.
I was wondering if there is any way to view a table of values corresponding to the plots of the electronic properties such as band structure, and conductance versus magnetic field for Hall effect systems.
Regards,
James

Hi Ravish,
This is where you are supposed to start.
http://kwant-project.org/doc/1/tutorial/
And of course this paper
http://downloads.kwant-project.org/doc/kwant-paper.pdf
This section will give you an idea how to 'tell' KWANT your Hamiltonian.
http://kwant-project.org/doc/1/tutorial/tutorial1
Now you must realise KWANT is not DFT, so optimisation or relaxation does
not appear in the picture. It is the geometry rather than the coordinate
that really matters. I would suggest to go through some basic tight binding
text before you jump into KWANT. And remember, the most essential part of
tight binding model is the Hamiltonian.
--
Sumit Ghosh
Spintronics Theory Group
PSE Division
KAUST
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Dear All,
I am new to kwant and wanted to know if there is any need of knowing the
Hamiltonian of the sample? Or what all I need other than the coordinates of
the atoms, to get started?
Regards