Dear All,
I am using Kwant to calculate the conductance of a Graphene structure. However,
it gives different conductance each time I run the code. I didn't change the
code. For the same code, I am getting different results each time. Is there
some error in my code or am I using the kwant function incorrectly? Please Help
Code
-----------
import kwant
import matplotlib.pyplot as plt
Wnr = 99
lnr = 60
a = 2.46
lat = kwant.lattice.honeycomb(a,norbs=1)
a,b = lat.sublattices
def make_sys():
def rect(pos):
x,y = pos
return 0<=x<=lnr and 0<=y<=Wnr
def delet(pos):
x, y = pos
return 0<=x<=35 and 20<=y<=80
model1 = kwant.Builder()
model1[lat.shape(rect,(1,1))] = 0
model1[lat.neighbors()] = 2.64
del model1[lat.shape(delet, (11,25))]
model1.eradicate_dangling()
return model1
def lead_attach(model1):
def lead1_shape(pos):
x, y = pos
return 0<y<=20
def lead2_shape(pos):
x, y = pos
return 80<=y<=Wnr
sym = kwant.TranslationalSymmetry(lat.vec((-1,0))) #from the left
sym.add_site_family(lat.sublattices[0], other_vectors=[(-1, 2)])
sym.add_site_family(lat.sublattices[1], other_vectors=[(-1, 2)])
lead = kwant.Builder(sym)
lead[lat.shape(lead1_shape, (1,2))]=0
lead[lat.neighbors()] =2.64
model1.attach_lead(lead)
########### lead 2 #################
sym1 = kwant.TranslationalSymmetry(lat.vec((-1,0))) #from the left
sym1.add_site_family(lat.sublattices[0], other_vectors=[(-1, 2)])
sym1.add_site_family(lat.sublattices[1], other_vectors=[(-1, 2)])
lead2 = kwant.Builder(sym1)
lead2[lat.shape(lead2_shape, (2,82))] = 0
lead2[lat.neighbors()] = 2.64
model1.attach_lead(lead)
model1.attach_lead(lead2)
kwant.plot(model1)
return model1
def dos_eng(model1):
rho = kwant.kpm.SpectralDensity(model1)
eng1, densities = rho.energies, rho.densities
return eng1, densities
def calc_conductance(sys, energies):
data = []
for energy in energies:
smatrix = kwant.smatrix(sys, energy)
data.append(smatrix.transmission(1, 0))
plt.figure()
plt.plot(energies, data)
plt.xlim([-3,3])
plt.ylim([0,4])
plt.xlabel("Energy (eV)",fontweight='bold')
plt.ylabel("Conductance $(e^2/h)$",fontweight='bold')
return data
def main():
sys = make_sys()
syst = lead_attach(sys)
syst = syst.finalized()
eng1, densities = dos_eng(syst)
cond = calc_conductance(syst,eng1)
if __name__ == '__main__':
main()
