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 users,
we have posted new instructions for installing kwant on Windows on the
kwant website: http://www.kwant-project.org/install
The old instructions do not work any more, as the format of the python
packages on Christoph Gohlke's webpage have changed.
Best regards,
the kwant team

Hi all,
firstly, thanks so much for your work in developing and maintaining kwant.
Hugely appreciated.
Is there any chance you could package it for {,k,x}ubuntu 15.04? I tried
installing kwant in that linux today, using the 14.10 package, and I am
getting a bunch of errors from Tkinter and matplotlib when I use kwant's
inbuilt plotter.
Many thanks for your help
David

Dear Christoph,
I use the following construction to connect the incommensurate
lattices: lat_e (graphene) and lat_e1 (square)
for x in list(lat_e1.shape(rectangle1, (0, 0))()):
for neighbour in lat_e.sublattices[0].n_closest(x.pos):
sys[(x, lat_e.sublattices[0](*neighbour))] = t01
for neighbour in lat_e.sublattices[1].n_closest(x.pos):
sys[(x, lat_e.sublattices[1](*neighbour))] = t01
I hope it's clear why I want to improve n_closest
Probably I can do that myself.
The above construction may indeed be in the core of readymade function
to connect
the two lattices.
Best wishes,
Sergey

Dear Joe,
Thanks, it is very useful for me. I want to know more about how the
transmission is related to the wave vector kx, because I want to calculate
the transmission contributed from some scale like kx=0~pi. So, how can i
know the wave vector for "2" in S10[3, 2] ? I tried "modes =
Smatrix.lead_info", it seems that it does not give the kx information. I
can take graphene as an example, we have two valleys K and K' in graphene.
Since the wave vectors kx for the two valleys are different, we can
calculate the transmission contributed from K valley and K' valley
separately, but of course we need to know "transmission-mode-kx" first.
Maybe this can be easily solved in another way.
Kwok-Long Lee
On Fri, Feb 6, 2015 at 8:03 PM, <kwant-discuss-request(a)kwant-project.org>
wrote:
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> Today's Topics:
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> 1. Transmission of each propagating mode (Lee Kwok-Long)
> 2. Re: Transmission of each propagating mode (Joseph Weston)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 6 Feb 2015 16:43:23 +0800
> From: Lee Kwok-Long <kwoklonglee(a)gmail.com>
> To: kwant-discuss(a)kwant-project.org
> Subject: [Kwant] Transmission of each propagating mode
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>
> Dear all,
> I want to calculate the transmission of each propagating mode separately,
> but I do not know how the propagating modes are related to the scattering
> matrix. For example, we can read from the bandstructure and find a mode at
> E=0.2，kx=0.95pi, how to find the transmission for this mode. Or, we have
> the transmission and how to find the contributions from each mode? Thanks
> in advance!
> Kwok-Long Lee
>

Dear all,
Since I used NEGF in my previous study, I want to use Green's function in
Kwant. I have tried a simple Kwant program to check my understanding of
"kwant.greens_function" and "lead.selfenergy(energy)", but it gives wrong
results. I used Fisher-Lee relation to calculate the conductance:
G = kwant.greens_function(sys, energy)
Gr=G.submatrix(1,0) # r indicates retarded
Ga=conj((Gr).T) # a indicates advanced
Sigma_Lr =flead0.selfenergy(energy) #r indicates retarded
Sigma_La =conj((Sigma_Lr).T) #a indicates advanced
Sigma_Rr =flead1.selfenergy(energy)
Sigma_Ra =conj((Sigma_Rr).T)
Gamma_in =1j*(Sigma_Lr-Sigma_La)
Gamma_out=1j*(Sigma_Rr-Sigma_Ra)
#TM=Gamma_out*Gr*Gamma_in*Ga
TM=Np.dot(Np.dot(Np.dot(Gamma_out,Gr),Gamma_in),Ga) #Fisher-Lee relation
data.append(real(Np.trace(TM)))
#Fisher-Lee relation
Do I do I misunderstand anything? Can you please find my mistakes? My Kwant
program code is attached at the end of this email. Thanks in advance!
Best wishes,
Weiyuan Tong

Dear authors,
I am sorry that I did not express it clear in my last email. For a 4 lead
system,
we have T30=smatrix.submatrix(3,0), T20=smatrix.submatrix(2,0) they all
include all the propagating modes. What I want is: for each propagating
mode like kx=2.9，we have the elements T30(3,3) and also the elements in T20.
If T30 and T20 are all arranged by propagating modes, it may be very easy,
T30(i,i) and T20(i,i) are for the same propagating mode. So, is there a
method to output T30(i,j) and T20(i,j) with the same propagating mode?
Regards,
Kwok-Long Lee

Hi
I want to calculate local density of states for tunneling into a spinful
superconductor. I have followed the example in the tutorial to set up
superconducting transport problem:
http://kwant-project.org/doc/1.0/tutorial/tutorial5
I was wondering if I could find the LDOS at a given site by first seperating
particle and hole contributions with:
a,b = np.split(kwant.ldos(sys,l),2)
And then add particle and hole contributions with np.add(a,b) and sum over
the spin parts with:
np.sum(np.add(a,b).reshape(-1,2),axis=1)
thanks
Amit

Dear authors,
I found a description for the greens_function in the Kwant document: "This
function can be used to calculate the conductance and other transport
properties of a system", so, we can also use the fisher-lee relation to
calculate the conductance in Kwant?
I read from Joe's reply email that the Green's function can be used like:
G = kwant.greens_function(sys, energy)
G.submatrix(1, 0) # from lead 0 to lead 1
this is the retarded Green's function? So the advanced Green's function is
G'=[G]+?
How to calculate the self-energy for lead 0 and lead 1?
Since there is no example in the tutorial, can you give us some suggestions
or simple examples?
Best wishes,
Weiyuan Tong

Dear Authors,
Thank you very much for supplying a so powerful tool to study the quantum systems. A series of complex physical phenomena can be modeled by Kwant.
I would like use the Kwant to calculate the charge density in a quantum wire. I met some trouble in understanding the output of retarded Green function when I use the module with the name of “kwant.solvers. default.green_function.” Assume we consider an ideal quantum wire, which includes two leads and a scattering region. The width of scattering regime is identical to the leads. The scattering region has 4*3 discrete points. The total green function should be a 12*12 matrix and contain 144 elements. However, I only got 6 by 6 matrix and 36 elements. What am I missing?
My code was the same as the code of the first example for quantum wire in page 16 in kwant document but with L=4 and W=3, energy = 1 and call for the module.
greenf=kwant.solvers.default.greens_function(sys, energy)
print greenf
Outputs are:
GreensFunction(data=array([[-0.28713703-0.20513305j, 0.08984532-0.29010194j,
0.16007656-0.20513305j, 0.26900184+0.11162436j,
0.20092781+0.07893034j, 0.17600545+0.07893034j],
[ 0.08984532-0.29010194j, -0.12706047-0.4102661j ,
0.08984532-0.29010194j, 0.37693326+0.15786068j,
0.26900184+0.11162436j, 0.26900184+0.11162436j],
[ 0.16007656-0.20513305j, 0.08984532-0.29010194j,
-0.28713703-0.20513305j, 0.26900184+0.11162436j,
0.17600545+0.07893034j, 0.20092781+0.07893034j],
[ 0.26900184+0.11162436j, 0.37693326+0.15786068j,
0.26900184+0.11162436j, -0.12706047-0.4102661j ,
0.08984532-0.29010194j, 0.08984532-0.29010194j],
[ 0.20092781+0.07893034j, 0.26900184+0.11162436j,
0.17600545+0.07893034j, 0.08984532-0.29010194j,
-0.28713703-0.20513305j, 0.16007656-0.20513305j],
[ 0.17600545+0.07893034j, 0.26900184+0.11162436j,
0.20092781+0.07893034j, 0.08984532-0.29010194j,
0.16007656-0.20513305j, -0.28713703-0.20513305j]]),
**************************************************************************************************************************
**************************************************************************************************************************
lead_info=[array([[-0.44909123-0.15234015j, -0.19564002-0.21544151j,
-0.06712522-0.15234015j],
[-0.19564002-0.21544151j, -0.51621644-0.3046803j ,
-0.19564002-0.21544151j],
[-0.06712522-0.15234015j, -0.19564002-0.21544151j,
-0.44909123-0.15234015j]]), array([[-0.51621644-0.3046803j , -0.19564002-0.21544151j,
-0.19564002-0.21544151j],
[-0.19564002-0.21544151j, -0.44909123-0.15234015j,
-0.06712522-0.15234015j],
[-0.19564002-0.21544151j, -0.06712522-0.15234015j,
-0.44909123-0.15234015j]])], out_leads=[0, 1], in_leads=[0, 1])
Regards,
Hang