% Atomic spacing
a = 5e-10;
% 
t = -1;
E_0 = 0;

N = 100;
k = linspace(- pi / a, pi / a, N);

e_k = E_0 + 2* t * cos(k*a);

figure(1);
plot(k, e_k, 'k-');
grid on;
xlabel('k');
ylabel('E[k] (eV)');