Now from the tight binding perspective

E(k) = EA  - a – 2 t cos ka , y(f) = c eimf m = 0, !1, ! 2, 3 (only six states)    k = mp/3a

k =  p/a

k =  2p/3a

k =  p/3a

Now consider: Poly(p-phenylene)

k =  0