Band structure silicene nanoribbons

[anahita]

I've written the following program for drawing the band structure Silicene nanoribbons, but in a zero energy building is a straight line.
Can help me to fixed problem.
% tight binding calculations for zgnr

clear;
clc;
close all;

NU=14; % Number of atoms in unit cell
Nbnd=4*NU; % number of bands
aa=2.28;
a=3.86;

X(1)=1.9745;
Y(1)=0;

xswitch = 0;

for ixy=2:NU
if mod(ixy,2)==1
Y(ixy)=Y(ixy-1)+aa;
else
Y(ixy)=Y(ixy-1)+aa*sind(30);

X(ixy) = xswitch;

if (ixy+1)<=NU
X(ixy+1)=xswitch;
end

if xswitch == 0
xswitch =aa*cosd(30);
else
xswitch = 0;
end
end
end

for iz=1:NU
if mod(iz,2)==1
Z(iz)=0.46152;
else
Z(iz)=0;
end

end

sho=0;
for is=[0,-1,1]
for ks=1:NU
sho=sho+1;
XT(sho)=X(ks)+is*a;
YT(sho)=Y(ks);
ZT(sho)=Z(ks);
Ax(sho)=is*a;
No(sho)=ks;
end
end
figure(1)
plot(XT,YT,'*')
Ax=Ax/a;for ik=1:101
K(ik)=-pi+(ik-1)*((2*pi)/100);

H=H0(Nbnd);

for is=1:NU
for js=1:sho
dis=sqrt(((XT(is)-XT(js))^2)+((YT(is)-YT(js))^2));
if abs(dis-2.232)<0.1 & abs(No(is)-No(js))>0
l=(XT(is)-XT(js))/dis;
m=(YT(is)-YT(js))/dis;
n=(ZT(is)-ZT(js))/dis;
h=hamiltonian(l,m,n);

H((No(is)-1)*4+1:No(is)*4,(No(js)-1)*4+1:No(js)*4)=H((No(is)-1)*4+1:No(is)*4,(No(js)-1)*4+1:No(js)*4)+h*exp(i*K(ik)*Ax(js));

end
end

end

E(ik,1:Nbnd)=sort(real(eig(H)));pl(ik)=(ik-1)/100;
end

figure(2)
plot(E)

 

[BigJDubs]

xlabel('k')ylabel('Energey (eV)')function H=H0(Nbnd)H=zeros(Nbnd,Nbnd);for i=1:NbndH(i,i)=0;endendfunction h=hamiltonian(l,m,n)h=zeros(4,4);for ia=1:4for ib=1:4if ia==ibh(ia,ib)=0;elseif ia==1h(ia,ib)=gamma(l,m,n);elseif ia==2h(ia,ib)=gamma(m,-l,n);elseif ia==3h(ia,ib)=gamma(-l,-m,n);elseif ia==4h(ia,ib)=gamma(-m,l,n);endendendendendfunction g=gamma(l,m,n)if l^2+m^2+n^2<=1if n>=0g= 0.012*((1+(l^2+m^2)/2)+sqrt(3)*l*m);elseg= 0.012*((1+(l^2+m^2)/2)-sqrt(3)*l*m);endelseg=0;endend