I don’t understand the purpose of including the omega_plus term resulting in w = 2 sqrt(kappa/m) |cos(ka/4)| in the final answer. Becuase this would represent the optical dipersion relation which doesn’t exist in the 1D monotomic chain right?
In the answer the following is stated: We observe that this is identical to the dispersion of the monatomic chain derived in the tight-binding lecture, but folded back into the 1st Brillouin zone because the unit cell is twice as large.
But when i plot the results i see that the omega_min term overlaps perfeclty with the monotomic chain. And i don’t really see how you can ‘fold back’ the omega_plus term to also overlap with the monotomic dispersion
