Hi,

I want to add two leads on left instead. I have attached two leads and try to find conductance and compare with just one lead on left. The results for two leads and just one lead is not same. Can you help me what I am doing wrong here?

I have attached my code here. 

import kwant                      # Recursive green function method 

import numpy as np                # Module with advanced math commands

from matplotlib import pyplot

from numpy import sqrt

from math import *

#======================================================================

# Define the shape -------------------

#======================================================================

def wv_shape(pos):

    x, y = pos

    return (np.abs(2.0*x)<=L)&(np.abs(y)<W1/2.0)    

#----------------------------------------------------------------------

a      = 1;     # Lattice constant 

t      = 1;     # Coupling between sites

E0L    = 0*t    # On-site potential in the lead

L      = 18;  # Length of the 

W1   = 90;  # Width on the left 

# Define geometry --------------------------------------------------------------------------

sys0 = kwant.Builder()

lat  = kwant.lattice.square(a)

#--------------------------------------------------------------------------------------------

# Define onsite energies and couplings  ----------------------------------------------------

sys0[lat.shape(wv_shape,(0,0))] = E0     # To make all sites the same

sys0[lat.neighbors()]           = t 

#--------------------------------------------------------------------------------------------

# Left lead ----------------------------------------------------------------------------------

left_lead1 = kwant.Builder(kwant.TranslationalSymmetry([-1,0]))   # The lead goes to minus infinity

left_lead2 = kwant.Builder(kwant.TranslationalSymmetry([-1,0]))   # The lead goes to minus infinity

left_lead1[(lat(0,y) for y in range(int(-W1/2+1),0))] = E0L    

left_lead2[(lat(0,y) for y in range(0,int(W1/2)))] = E0L    

left_lead1[lat.neighbors()] = t                                   # Couplings in the lead

left_lead2[lat.neighbors()] = t                                   # Couplings in the lead

sys0.attach_lead(left_lead1);

sys0.attach_lead(left_lead2);

#--------------------------------------------------------------------------------------------

# Right lead ---------------------------------------------------------------------------------

right_lead = kwant.Builder(kwant.TranslationalSymmetry([1,0]))   # The lead goes to plus infinity

right_lead[(lat(0,y) for y in range(int(-W1/2+1),int(W1/2)))] = E0L    

right_lead[lat.neighbors()] = t                                  # Couplings in the lead

sys0.attach_lead(right_lead);

#---------------------------------------------------------------------------------------------

sys = sys0.finalized()

kwant.plot(sys);                                             # Plots the shape

def plot_conductance(sys, energies):

    data = []

    for energy in energies:

        smatrix = kwant.smatrix(sys, energy)

        data.append(smatrix.transmission(2, 0)+smatrix.transmission(1,2) )

        #transmission from left 2 leads to right lead 

    pyplot.figure()

    pyplot.plot(energies, data)

    pyplot.xlabel("energy [t]")

    pyplot.ylabel("conductance [e^2/h]")

    pyplot.show()

energies=[-3+i*0.02 for i in range(100)]

plot_conductance(sys,energies)