Dear Lee,
All what you need is to express the equation of your path: I mean ky as a
function of kx on this path.
Please, find below an example about Graphene band structure. I compare it
to the analytical result found in literature.
Just be careful, when the lattice vectors are not orthogonal. You need to
do some transformation to get the vectors in the reciprocal lattice.
I wrote this a while ago, so please check it if there are no mistakes in
it. It works with kwant 1.3
I hope this helps
Adel
###############################
import numpy as np
from numpy import pi,sqrt,arccos
import kwant
from kwant.wraparound import wraparound,plot_2d_bands
from matplotlib import pyplot
import scipy
def make_graphene():
"""Create a builder for a periodic infinite sheet of graphene."""
lat = kwant.lattice.honeycomb()
sym = kwant.TranslationalSymmetry(lat.vec((1, 0)), lat.vec((0, 1)))
sys = kwant.Builder(sym)
sys[lat.shape(lambda p: True, (0, 0))] = 0
sys[lat.neighbors()] = 1
return sys
sys=make_graphene()
syst = wraparound(sys).finalized()
kwant.plot(sys)
plot_2d_bands(syst)
# calculate the reciprocal symmetry vectors: these
# are the columns of 'A'
sym=sys.symmetry
B = np.array(sym.periods).T
A = B.dot(np.linalg.inv(B.T.dot(B)))
# transforms a momentum in the basis (kx, ky) to the basis of
# reciprocal symmetry vectors
def momentum_to_lattice(k):
k, residuals = scipy.linalg.lstsq(A, k)[:2]
if np.any(abs(residuals) > 1e-7):
raise RuntimeError("Requested momentum doesn't correspond"
" to any lattice momentum.")
return k
def H_k(kx, ky):
k = (kx, ky)
k_prime = momentum_to_lattice(k)
return syst.hamiltonian_submatrix(args=k_prime)
# This function is the exact result taken from literature
def function(kx,ky):
return sqrt(3+2*np.cos(kx)+4*np.cos(kx/2.) *np.cos(sqrt(3)/2*ky))
# Here I am comparing the numerical result with the analytical result. with
kx varying from -pi to pi
k_val=np.linspace(-pi,pi,61)
ky=2*pi/sqrt(3)
resultat1=[abs(H_k(kx,ky)[0]) for kx in k_val]
resultat2=[abs(function(kx,ky)) for kx in k_val]
pyplot.plot(k_val,resultat1,'r-')
pyplot.plot(k_val,resultat2,'go')
pyplot.show()
#
#
# $
# E=\pm t \sqrt{3+2 \cos(\sqrt{3}k_x a)+a \cos(\frac{\sqrt{3}}{2}k_x a)
\cos(\frac{3}{2} k_y a)}
# $
#
# with $a=1/\sqrt{3}$
#
# The point $K$ is: $K(\frac{4\pi}{3\sqrt{3}a},0) $
# The point $M$ is: $M(\frac{\pi}{\sqrt{3} a},\frac{\pi}{3 a})$
# In[ ]:
def eigenvalues(kx,ky):
return np.sort(np.linalg.eigvalsh(H_k(kx, ky)))
nb=30
d1=4*pi/3 # this is the distance when you go from Gamma to K
d2=2*pi/3 # this is the distance when you go from K to M
Kx1= np.linspace(0,4*pi/3,nb)
Result1=np.array([eigenvalues(kx,0) for kx in Kx1])
Kx2=[d1 + sqrt((kx - (4*pi/3))**2 + 3*(kx - 4*pi/3)**2) for kx in
np.linspace(pi,4*pi/3,nb)] #distance Gamma K is added here
Result2=np.array([eigenvalues(kx,-sqrt(3)*(kx - 4.* pi/3)) for kx in
np.linspace(pi,4*pi/3,nb)])
Kx3=[d1 + d2 + sqrt((x - pi)**2 + (1/sqrt(3)* x - pi/sqrt(3))**2) for x in
np.linspace(0,pi,nb)]##3distance Gamma K M is addded here
Result3=np.array([eigenvalues(kx, 1./sqrt(3)* kx) for kx in
np.linspace(0,pi,nb)])
pyplot.scatter(Kx1,Result1[:,0],color='r')
pyplot.scatter(Kx2,Result2[:,0],color='g')
pyplot.scatter(Kx3,Result3[:,0],color='c')
pyplot.scatter(Kx1,Result1[:,1],color='r')
pyplot.scatter(Kx2,Result2[:,1],color='g')
pyplot.scatter(Kx3,Result3[:,1],color='c')
pyplot.show()
On Wed, Oct 24, 2018 at 7:53 PM kuangyia lee
Dear kwant developers and users,
I want to calculate and plot the band structure of bulk 2D material along some high-symmetry lines in the Brillouin zone (e.g. Gamma-->K-->M--Gamma), i.e. the 1D band structure.
I found that someone already posted a relevant issue and some useful solutions were also given. For example, see https://kwant-discuss.kwant-project.narkive.com/2fT27IJh/kwant-for-bulk-syst....
However, these solutions are only for calculating and plotting the full 2D band structure in the Brillouin zone.
Can anyone give some useful solutions to my concern? Your help is much appreciated.
Thank you and best regards, Kuangyia Lee
-- Abbout Adel