Kwant-discuss April 2022

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Re: Problem in calculation of Current density
by Ajit Kumar Sahu 11 Apr '22

11 Apr '22

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current-voltage diagram
by loojoo026＠gmail.com 08 Apr '22

08 Apr '22

dear all I have done my project using Kwant and I have drawn a conductance-energy diagram for the system. The question I have is how can I get the current-voltage diagram? thanks Leo

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Problem in calculation of Current density
by sahu.ajit92＠gmail.com 07 Apr '22

07 Apr '22

Dear all, I am new to kwant. I am trying to calculate the current density for different widths of zigzag graphene nanoribbon. But I am getting strange results for widths above 22 angstroms, there is slightly back propagation of current. I want to know, is there any mistake in my code or anything else to be considered for the calculation of current density. Here i am attaching the code with current density result for width 22 and 24 angstroms. In 24 angstroms, there is back propagation of current. Please help me. --------Code ---- import kwant import numpy as np from matplotlib import pyplot import matplotlib.pyplot as plt import numpy.linalg as npl import scipy.sparse.linalg as sla import os pi=np.pi ############################################## structure ######################## Wnr=22 lnr=180 ############# empty system kwant lat=kwant.lattice.honeycomb(a=2.46,norbs=1) a,b=lat.sublattices ########### functions for structure build def onsite(site, voltage): x, y = site.pos return voltage def rect(pos): x,y=pos return 0<x<=lnr and 0<y<=Wnr ################################ main structure i.e. rectangle #################### model1 = kwant.Builder() model1[lat.shape(rect,(1,1))] = 0 model1[lat.neighbors()] =2.64 model1.eradicate_dangling() kwant.plot(model1) ############### functions for lead structure build ################################ def lead1_shape(pos): x, y = pos return 0<y <=Wnr ############first lead codes########## 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, (0,1))]=onsite lead[lat.neighbors()] =2.64 #########attaching the lead to model1 model1.attach_lead(lead) model1.attach_lead(lead.reversed()) #second lead attach in reverse manner model1=model1.finalized() kwant.plot(model1) ####################### calculations ############################ ###functions for calculations params = dict(voltage=0) kwant.plotter.bands(model1.leads[1],params=params) #bandstructure of lead def plot_conductance(sys, energies,params): # Compute transmission as a function of energy data = [] for energy in energies: smatrix = kwant.smatrix(sys, energy, params=params) data.append(smatrix.transmission(0, 1)) pyplot.figure() pyplot.plot(energies, data) #pyplot.xlim([-2,2]) #pyplot.ylim([0,6]) pyplot.xlabel("energy [t]") pyplot.ylabel("conductance [e^2/h]") pyplot.show() return data ##########DOS KPM################# rho = kwant.kpm.SpectralDensity(model1,params=params) energies, densities = rho.energies, rho.densities plt.figure() plt.plot(energies, densities) ##################################### #######conductance w.r.t energy############## data=plot_conductance(model1,energies, params) ####################### ###########current density######## J_0 = kwant.operator.Current(model1) wf = kwant.wave_function(model1,energy=1,params=params) wfs=wf(0) wfs_of_lead_2 = wf(1) psi = wf(0)[0] current = J_0(psi) kwant.plotter.current(model1, current, colorbar=True) ################################################ please find the current density result in the link https://drive.google.com/file/d/1j8A6yZbZwaR1yAi3gKnuZalJYTJ8FQHc/view?usp=… https://drive.google.com/file/d/155-PxKLLCtGewqQL2fuitGWPI6KCReik/view?usp=…

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Kwant-discuss April 2022