Dear Sahu,
The KPM method is based on a probabilistic algorithm. Each time you run the
code the set of energies that you get is different. Since, you are
calculating the conductance at the energies provided by the KPM method, you
will of course get different values for each run.
In different words:
rho = kwant.kpm.SpectralDensity(model1)
eng1, densities = rho.energies, rho.densities
eng1 is different between two different runs of the program.
I hope this helps,
Adel
On Tue, Dec 13, 2022 at 9:18 AM <sahu.aji...@gmail.com> wrote:
> 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()
>
--
Abbout Adel
