Dear Ran, I am not sure what you mean by « the real energy values of the system »: the system has indeed a width W but no length, it is infinite along the other direction. How the system is separated between a finite central region and the leads is totally arbitrary (and should not affect the results). The results should not be affected by the particular points you pick on the Transmision versus Energy curve. However, beware of the energy units. In the example, the hopping between sites has been set to 1. In a scheme where you discretize the Schrodinger equation, it means that you energy unit is hbar^2/(2 m a^2) where a is the discretization step (in meter). If you want to get the discrete energies of the finite system, just don’t attach the leads and diagonalize the obtained Hamiltonian as shown in https://kwant-project.org/doc/1/tutorial/spectrum https://kwant-project.org/doc/1/tutorial/spectrum (for a different system). You will get a spectrum E = 2 cos (pi*nx/W) + 2 cos (pi*ny/L) which matches your spectrum for small nx and ny when using the correct units. Happy kwanting, Xavier

Le 12 janv. 2019 à 17:03, mutcran a écrit :

Hi,

For the calculation of the conductance in the tutorial file “quantum_wire_revisited.py”, instead of giving arbitrary energies like [0.01 * i for i in range(100)], can I give the real energy values of the system by:

E=(pi^2*hbar^2)/(2m)*(nx^2/L^2+ny^2/W^2)

where I took transport direction length (L) as very long, say 100 times larger than the width (W). (Since the transport direction is practically open in KWANT)

This gives very different results than using arbitrary energies. What is the problem with this approach and is there a way to explicitly account the discrete energies of the system (not the arbitrary ones)?

Best,

Ran