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 Kwant developer,
Thank you for your effort in developing Kwant.
I have a question about the definition of the direction of momentum in the smatrix.lead_info. Assume a lead lies along the y direction with primitive vector (0,1). The symmetry operation of a lead is (0,1) if the lead goes towards the positive direction and is (0,-1) if the lead goes towards the negative direction. For the momenta contained in smatrix.lead_info for these two leads , do they use the same coordinate system? Positive momenta mean the direction (0,1), negative momenta mean the direction (0,-1). For velocity, in smatrix.lead_info, it has nothing to do with the coordinate system. Positive means outgoing, negative means incoming in the lead.
Thank you
KS Chan
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Dear all,
I have tried a primitive forking of kwant computation with joblib
package. This worked well for bands computation, here's the code, but
it fails for smatrix.transmission. I would be grateful for any hints
and examples.
Thank you,
Sergey
from joblib import Parallel, delayed
def plot_bandstructure(flead, momenta, args, max=0.05):
global processors
switch=False
cutoff=0.001
bands = kwant.physics.Bands(flead, args=args)
energies = Parallel(n_jobs=processors)(delayed(bands)(k) for k in
momenta)
pyplot.figure()
pyplot.plot(momenta, energies)
pyplot.ylim([-max,max])
pyplot.xlabel("momentum [(lattice constant)^-1]")
pyplot.ylabel("energy [t]")
pyplot.show(block=False)
def transm(sys, energy, lead1,lead2,args):
print("Smatrix for energy ", energy)
smatrix = delayed(kwant.smatrix)(sys, energy,args=args)
return smatrix.transmission(lead1, lead2)
def plot_conductance(sys, lead1,lead2, energies,args,label):
# Compute transmission as a function of energy
global processors
data = Parallel(n_jobs=processors)(delayed(transm)(sys,
energy,lead1, lead2, args=args) for energy in energies)
print(data)
pyplot.figure()
pyplot.plot(energies, data)
pyplot.xlabel("energy [t]")
pyplot.ylabel("conductance [e^2/h]")
pyplot.title(label)
return data

Respected Sir,
It's Biswadeep Upadhyay from India. I'm a engineering student recently
studying in 3rd year. I'm pursuing a study of Nano Device under the
guidance of my professor specialized in Electronic devices. In that regard
I consistently use the Kwant software. Recently my area of focus is Carbon
Nano Tubes(CNTs). I have done several simulations on 2D structures earlier
with ease. But I have question can i simulate CNTs using Kwant. More
precisely will I be able to solve CNT related problem using Kwant ; for
example to plot the system , band structure, plot of conductance.
So I request you to have a look upon my query and enlighten me in this
regard. Your active operation is highly solicited.
Regards,
Biswadeep

Hi Everyone!
I want to solve basic problem of transmission of electron through a
potential barrier without taking into account any effects contacts. But the
influence of leads in all the examples provided in kwant documentation
definitely exists. For example, in the quantum wire case leads are set the
same way as the scattering region, that why I expect the transmission
should be obtained identically one (for any energy of incident electron).
This means that kwant takes into account also some regions outside the
leads e.g. bulk metal contacts.
Also I modified the quantum well example like this:
def plot_transmission(syst, energies, welldepth):
data = []
for energy in energies:
smatrix = kwant.smatrix(syst, energy, args=[-welldepth])
data.append(smatrix.transmission(1, 0))
data = np.array( data )
pyplot.figure()
pyplot.plot(energies, data)
pyplot.xlabel("Energy [t]")
pyplot.ylabel("Transmission")
pyplot.show()
and in the main function make a call
plot_transmission(syst, [0.01 * i for i in range(1,100)], 0.0)
As a result some dependence on E is obtained even for the case of zero
depth of the potential whell and it is not identically one.
So, is it possible to obtain in Kwant the transmission coefficient through
the defined in the scattering region structures which is not affected by
anything else?
Sincerely,
Jambulat Basaev

Dear Kwant team,
(am using the development version, 1.3)
I am trying to plot the potential of my system and I want to use the hamiltonian(ind,ind,*args) function, but I don't understand how to use the args. Normally, I would give a vector with the values of the args as input, but this doesn't work in the case of hamiltonian (it does with hamiltonian_submatrix). What am I doing wrong?
I also have a problem using the kwant.plot(sys) after I switched to Linux, I get the error message "NameError: name 'mplot3d' is not defined", is there something I need to install?
Sincerely,
Camilla

In the discussion thread about calculation of current density, it is mentioned for the function defined for current as follows only work for 1 orbital per site. Does the expression work for system with spin? I guess the Hamiltonian matrix element for sites I and j will be a matrix for a system with spin and the wavefunction for a site is a vector.
If this is the case, the function still works for systems with spin degree of freedom (or other internal degree of freedom)
Ks chan
def current(psi):
H_ij = sys.hamiltonian(i, j, args=(B,))
return -2 * (psi[i].conjugate() * H_ij * psi[j]).imag
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Hi Everyone!
I want to solve basic problem of transmission of the electron through a potential barrier without taking into account any effects contacts. But the influence of leads in all the examples provided in kwant documentation definitely exists. For example, in the quantum wire case leads are set the same way as the scattering region, that why I expect the transmission should be obtained identically zero. This means that kwant takes into account also some regions outside the leads e.g. bulk metal contacts.
Also I modified the quantum well example like this:
def plot_transmission(syst, energies, welldepth):
data = []
for energy in energies:
smatrix = kwant.smatrix(syst, energy, args=[-welldepth])
data.append(smatrix.transmission(1, 0))
data = np.array( data )
pyplot.figure()
pyplot.plot(energies, data)
pyplot.xlabel("Energy [t]")
pyplot.ylabel("Transmission")
pyplot.show() and in the main function make a call
plot_transmission(syst, [0.01 * i for i in range(1,100)], 0.0)
As a result some dependence on E is obtained even for the case of zero depth of the potential whell and it is not identically zero.
So, is it possible to obtain in Kwant the transmission coefficients through the defined in the scattering region structures which is not affected by anything else?
Sincerely,
Jambulat

Dear Colleagues,
There has already been a discussion on this subject back in 2014,
(https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00124.html)
but I am not quite sure I understand the proper solution.
I made a lead with rectangular unit cell and naive attempt to make
periodic boundary conditions gives a error:
"Further-than-nearest-neighbor cells are connected by hopping". The only
solution I can think of, is to introduce an auxiliary 1-D lattice made
of the atoms along the edge and
introduce hopping from this 1D chain to the edge atoms of 2D lead. Hope
it will work. Are there any better solutions?
Thanks,
Sergey

Dear all,
Can anyone send an example of setting periodic boundary conditions on
a lead, please. E.g. on a simplest square lattice.
Is defining a long unit cell the only solution?
Thanks,
Sergey