Hello. 

My name is Daehan Park. I am a new user for Kwant. 

To accustom me to using Kwant, I start to attack simple quantum mechanics problems in kwant program. 

In below code, I try to solve a simple square barrier problem.

==================================================================

import kwant
import math
from matplotlib import pyplot
syst = kwant.Builder()

wire = kwant.lattice.chain(1)

t = 1.0       # hopping parameter
W = 100    # the number of atoms in the direction of width

for i in range(W):
    # on-site Hamiltonian
    syst[(wire(i))]=2*t

for i in range(10):
    # on-site Hamiltonian
    syst[(wire(i+10))]=2*t + 0.5
 
syst[wire.neighbors()] = -t     # hopping

# attaching leads 

sys_left_lead = kwant.TranslationalSymmetry([-1])  
left_lead = kwant.Builder(sys_left_lead)

left_lead[wire(0)] =  2*t
left_lead[wire.neighbors()] = -t
syst.attach_lead(left_lead)
syst.attach_lead(left_lead.reversed())

kwant.plot(syst)
sys = syst.finalized()

def plot_conductance(sys, energies):
    # Compute conductance
    data = []
    for energy in energies:
        smatrix = kwant.smatrix(sys, energy)
        data.append(smatrix.transmission(1, 0))

    pyplot.figure()
    pyplot.plot(energies, data)
    pyplot.xlabel("energy [t]")
    pyplot.ylabel("conductance [e^2/h]")
    pyplot.show()

plot_conductance(sys, energies=[0.01* i + 1e-6 for i in range(500)])

========================================================================

The outcome above the code is as following;

 

My question is why conductance becomes zero when the incident energy is over 4.

Thank you for reading my e-mail