Abbout Adel wrote:
> Dear Sahu,
> What you see is just a flat band. It doesn't mean that there is an error in
> the code.
> Actually, it is very common to see it in graphene for example if you have
> dangling sites in an infinite stripe.
> You need of course to avoid that energy in the calculation of the
> scattering matrix because it is singular.
> I hope this helps,
> Adel
> On Fri, Oct 14, 2022 at 11:26 AM sahu.aji...@gmail.com wrote:
> > Dear all,
> > I make AGNR in Kwant and introduce the defect in both the scattering
> > region and lead.
> > When plotting the bandstructure of the lead there is a straight line that
> > comes at E=0.
> > I am confused that there is some error in the code or not. Please help
> > Thanking You
> > code-
> > ________________
> > import kwant
> > import numpy as np
> > import matplotlib.pyplot as plt
> > pi = np.pi
> > a = 1
> > d = 1.42;
> > a1 = d*np.sqrt(3);
> > lat = kwant.lattice.general(
> > [[a1, 0], [a1/2, a1*np.sqrt(3)/2]],[[0, 0], [0, a1/np.sqrt(3)]]
> > )
> > a,b = lat.sublattices
> > def set_pub(): # for plotting the figures
> > plt.rcParams.update({
> > "font.weight": "bold", # bold fonts
> > "font.size":18,
> > #"tick.labelsize": 15, # large tick labels
> > "lines.linewidth": 2, # thick lines
> > "lines.color": "k", # black lines
> > "grid.color": "0.5", # gray gridlines
> > "grid.linestyle": "-", # solid gridlines
> > "grid.linewidth": 0.5, # thin gridlines
> > "xtick.major.size":10,
> > "xtick.minor.size":5,
> > "ytick.major.size":10,
> > "ytick.minor.size":5,
> > "savefig.dpi": 600, # higher resolution output.
> > })
> > def make_sys(w,l):
> > def rect(pos):
> > x,y = pos
> > return -w*a1<x<w*a1 and -l*a1<y<l*a1
> > model1 = kwant.Builder()
> > model1[lat.shape(rect,(1,1))] = 0
> > model1[lat.neighbors()] = 2.46
> > return model1
> > def lead_join(model1,w):
> > def lead_shape(pos):
> > x, y = pos
> > return -w*a1<x<w*a1
> > Num = 8*(a1*np.sqrt(3)/2)
> > sym = kwant.TranslationalSymmetry([0,Num])
> > lead = kwant.Builder(sym)
> > lead[lat.shape(lead_shape, (1,1))] = 0
> > lead[lat.neighbors()] = 2.46
> > model1.attach_lead(lead)
> > model1.attach_lead(lead.reversed())
> > return model1,lead
> > def defect(model1,lead):
> > def delet_lead(pos, shift = +a1*np.sqrt(3)):
> > x, y = pos
> > z=x**2+(y-shift)**2
> > return z<(a1)**2
> > def delet_str(pos, shift = a1*np.sqrt(3)):
> > x, y = pos
> > z = x**2 + (y-shift)**2
> > return z<(a1)**2#z<(2*a1)**2
> > del model1[lat.shape(delet_str, (1,1))]
> > del lead[lat.shape(delet_lead, (2,2))]
> > kwant.plot(model1)
> > set_pub()
> > plt.rc('axes', linewidth = 2.0)
> > plt.show()
> > return model1
> > def plot_bandstructure(flead, momenta):
> > bands = kwant.physics.Bands(flead)
> > energies = [bands(k) for k in momenta]
> > band_gap = 100
> > for k in momenta:
> > for band in bands(k):
> > if(band <0):
> > #Lower than fermi band
> > min_band=band
> > else:
> > max_band=band
> > if(max_band-min_band<band_gap):
> > band_gap=max_band-min_band
> > break
> > print("Gap Energy= " + str(band_gap) +" ev ")
> > kwant.plotter.bands(flead) # bandstructure of lead
> > plt.ylim([-3,3])
> > set_pub()
> > plt.xlabel("K $(\AA^{-1})$",fontweight='bold')
> > plt.ylabel("Energy (eV)",fontweight='bold')
> > plt.show()
> > return band_gap
> > def main():
> > w = 5
> > l = 8
> > sys = make_sys(w,l)
> > syst,lead = lead_join(sys,w)
> > syst = defect(syst,lead)
> > fsys = syst.finalized()
> > momenta = [-pi + 0.02 * pi * i for i in range(101)]
> > Band_Gap = plot_bandstructure(lead.finalized(), momenta)
> > if __name__ == '__main__':
> > main()
> > --
> Abbout Adel
Thank You, cleared my doubts
