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

Hello,
In the system I use two lattices to represent spin up and down.
lat_u = kwant.lattice.honeycomb(a=1, name='up')
lat_d = kwant.lattice.honeycomb(a=1, name='down')
When I obtain the scattering wave functions from wf=kwant.wave_function(sys, en),
it contains the value for both lat_u and lat_d.
Is that possible to extract the wave function only for lat_u or lat_d?
I tried to separate the wave function based on the odd/even index, but it is not the right sequence.
Thank you in advance.
Regards,
Yuhao

Hi Leon,
Thank your for the kind suggestion. But can you show me how to get download
of your attached jupyter notebook. Thanks again !
Regards,
Kuangyia
On Wed, Oct 24, 2018 at 10:38 PM <kwant-discuss-request(a)kwant-project.org>
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> Today's Topics:
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> 1. plotting band structure of bulk 2D material along high
> symmetry lines in the Brillouin zone (kuangyia lee)
> 2. Re: plotting band structure of bulk 2D material along high
> symmetry lines in the Brillouin zone (Maurer, Leon)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 24 Oct 2018 18:52:49 +0200
> From: kuangyia lee <kuangyia.lee(a)gmail.com>
> To: kwant-discuss(a)kwant-project.org
> Subject: [Kwant] plotting band structure of bulk 2D material along
> high symmetry lines in the Brillouin zone
> Message-ID:
> <CAPVHYSmaFEHTHmKdh63u0RfWp+rJ15DP84bY==
> gG-v+93W8ncA(a)mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear kwant developers and users,
>
> I want to calculate and plot the band structure of bulk 2D material along
> some high-symmetry lines in the Brillouin zone (e.g. Gamma-->K-->M--Gamma),
> i.e. the 1D band structure.
>
> I found that someone already posted a relevant issue and some useful
> solutions were also given. For example, see
>
> https://kwant-discuss.kwant-project.narkive.com/2fT27IJh/kwant-for-bulk-sys…
> .
>
>
> However, these solutions are only for calculating and plotting the full 2D
> band structure in the Brillouin zone.
>
> Can anyone give some useful solutions to my concern? Your help is much
> appreciated.
>
> Thank you and best regards,
> Kuangyia Lee
>

Dear kwant developers and users,
I want to calculate and plot the band structure of bulk 2D material along
some high-symmetry lines in the Brillouin zone (e.g. Gamma-->K-->M--Gamma),
i.e. the 1D band structure.
I found that someone already posted a relevant issue and some useful
solutions were also given. For example, see
https://kwant-discuss.kwant-project.narkive.com/2fT27IJh/kwant-for-bulk-sys….
However, these solutions are only for calculating and plotting the full 2D
band structure in the Brillouin zone.
Can anyone give some useful solutions to my concern? Your help is much
appreciated.
Thank you and best regards,
Kuangyia Lee

Hi Kuangyia,
If I understand your question correctly, I have done this by extracting a Hamiltonian from the wrapped system using hamiltonian_submatrix (with whatever wavevector you want as an argument) and finding the eigenvalues of that matrix. I’ve attached a jupyter notebook that uses kwant to calculate Si’s band structure along high-symmetry directions. In the notebook, cell 6 is the relevant one. That said, others may know a cleaner way to do this.
That said, what is your ultimate goal? If it’s simply to compute band structures of a bulk material, then you can just write down the matrix without kwant and find its eigenvalues. (I’ve attached a second notebook that does that.) I don’t think that kwant simplifies the process. If you want to later want to do some transport simulation, then starting with kwant could prove useful.
-Leon
From: Kwant-discuss <kwant-discuss-bounces(a)kwant-project.org> on behalf of kuangyia lee <kuangyia.lee(a)gmail.com>
Date: Wednesday, October 24, 2018 at 10:53 AM
To: "kwant-discuss(a)kwant-project.org" <kwant-discuss(a)kwant-project.org>
Subject: [EXTERNAL] [Kwant] plotting band structure of bulk 2D material along high symmetry lines in the Brillouin zone
Dear kwant developers and users,
I want to calculate and plot the band structure of bulk 2D material along some high-symmetry lines in the Brillouin zone (e.g. Gamma-->K-->M--Gamma), i.e. the 1D band structure.
I found that someone already posted a relevant issue and some useful solutions were also given. For example, see https://kwant-discuss.kwant-project.narkive.com/2fT27IJh/kwant-for-bulk-sys….
However, these solutions are only for calculating and plotting the full 2D band structure in the Brillouin zone.
Can anyone give some useful solutions to my concern? Your help is much appreciated.
Thank you and best regards,
Kuangyia Lee

Dear Kwant developers,
I've found in other threads in the mailing list that the units of current is for example (unit of charge)/(hbar/unit of energy) (https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg01100.html). Also, the local density of states has units of energy/volume (https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00169.html?).
My question is, what is the units of the output of the density operator? Is it energy/volume as well? I ask this because intuitively I view it as the square of the wavefunction, but it gives me values larger than 1 for each site when there is only 1 mode involved (see attached picture) ?so it is not just the probability of findinge the electron at that site because this should be maximum 1. I have also noticed that the values I get in the colorbar depend on the value of my hopping (e.g. case of graphene), but overall I'm not so sure of the units.
Thank you again for your help.
Kind regards,
Marc

Dear all,
I am trying new Kwant 1.3 features on a very simple example of
graphene monolayer, and, apart from a standard well-working code I add:
for x in sys.sites(): x.family.norbs=1 for x in leadxp.sites():
x.family.norbs=1 for x in leadxm.sites(): x.family.norbs=1 (to avoid
norbs not defined error)
...
J_0 = kwant.operator.Current(sys) wf =
kwant.solvers.default.wave_function(sys, energy=0.01,
args=[phi,chempot,0]) psi=wf(1) current = J_0(psi)
I get the following suspicious message: The size of the file
/home/sergey/.local/lib/python3.6/site-packages/kwant/operator.cpython-36m-x86_64-linux-gnu.so
is 2734 KB. Do you really want to load it?
After answering yes, I get the error message, caused by current =
J_0(psi) :
"The debugged program raised the exception unhandled ValueError "vector
is incorrect shape" File:
/home/sergey/.local/lib/python3.6/site-packages/kwant/operator.cpython-36m-x86_64-linux-gnu.so,
Line: 529
Break here?"
Could anyone guess, what goes wrong?
N.B. I have installed Kwant with a command pip3 install kwant
Thanks,
Sergey

Dear Kwant developers,
I'm playing with the current maps and there is something I don't understand. I attatch a current plot of a 2 terminal-device of some edge states in a particular model of graphene (the current is the sum of all wavefunctions from the incoming lead which is positioned at the left). I understand thus that the arrows point from left to right, it's the current direction. But then, in one edge I have a stronger color meaning there is more current there, but on the other hand, in the other edge the arrow is thicker, which I assume it also represents more current. Does the arrow thickness and color represent the same thing and therefore both edges have the same current or do they represent different things and so I'm missing something? Could you please clarify this for me?
In addition, when I plot the spin current projected on the Z axis (as in Kwant's documentation), I assume that the direction of the arrow is for example where the spin-up electrons move, while the spin-down electrons move to the other direction. Is this correct?
Thank you in advance for your help.
Bests?,
Marc
------------------------
Marc Vila Tusell
La Caixa - Severo Ochoa PhD in the Theoretical and Computational Nanoscience Group
Catalan Institute of Nanoscience and Nanotechnology (ICN2)
Barcelona Institute of Science and Technology (BIST)
Additional information:
http://icn2.cat/en/theoretical-and-computational-nanoscience-grouphttps://www.researchgate.net/profile/Marc_Vila_Tusellhttps://www.becarioslacaixa.net/marc-vila-tusell-BI00042?nav=truehttps://orcid.org/0000-0001-9118-421X

Hello All,
I was wondering if there is a way in Kwant to combine two systems. For
example, lets say I build two systems sys1 and sys2 (on the kwant.plot
graph, the two systems do not overlap, i.e. they are separated by a finite
distance). Then, would it be possible to plot the two systems on the same
graph, and then calculate transmission of combined sys1+sys2?
Any help would be much appreciated.
Best Regards,
Shivang Agarwal
--
*Shivang Agarwal*
Senior Undergraduate
Coordinator - Academic Discussion Hours
Discipline of Electrical Engineering
IIT Gandhinagar
Contact: +91-9869321451

Hi all,
First time using a mailing list, sorry if I’ve done something annoying or stupid.
Anyway, is it possible (and sensible) to use Kwant for bosonic systems? I’m talking about systems where you have a tight-binding Hamiltonian, but the creation operators are bosonic.
For example, I would like to simulate the edge states in a chain of metallic nanoparticles (like in [1]), where I model each nanoparticle with a single dynamical degree of freedom describing the electric-dipole moment.
Thanks very much for any input,
Tom
[1] https://arxiv.org/pdf/1611.03349.pdf