Dear Kwant community,

Thanks for the quick reply.

I plot the band structure and I obtaine the figure I attached. For a free-particle I expect a band structure like quadratic dispersion (E \sim k^2). The plot of structure band is nearly quadraic. Is it due to discretization of the system ? So it means that the wave-function sent to the left lead (in my example) is not a free-plane-wave ? Is there a way to control the wave-function injected in the lead ?

Yours sincerely

Lorenzo Bagnsacco

Il giorno mar 18 gen 2022 alle ore 15:40 Anton Akhmerov <> ha scritto:
Hi Lorenzo,

You need to compute the transmission at an energy where the leads have modes. At E = 10 in your system there aren't any.

Plotting the band structure of the leads helps. Check out also the Kwant tutorial at


On Tue, 18 Jan 2022 at 15:37, Lorenzo BAGNASACCO <> wrote:
Dear Kwant community,

I am a physics student and I am approaching to Kwant to solve simple problems of scattering.
I am new in Kwant and, for this reason, I'm trying to use Kwnat for basic problems of scattering.
The most simple problem in my mind is the scattering of a plane-wave (1 dimension) from the left of a potential barrier. If we now suppose the potential barrier is 'zero' everywhere, the scattering matrix, according to the scattering theory, should be 'S={{0,1},{1,0}}'.
If I try to compute the reflection and transmission coefficient, I obtained the correct values (1 for reflection and 0 for transmission). But it occurs only for some energies. For example in the code I attached, if I put the value of '10' in  'S=kwant.solvers.default.smatrix(syst,10)' I obtaine for reflection and transmission the value of '0'. Where is my errors? And, is there a way to print the entire elements of the scattering matrix ?

Yours sincerely

Lorenzo Bagnasacco