When we introduced the contribution of phonon modes to the optical response of the materials we obtained: 61 1 601 6001 6001 _ le + 6+2 0+2 em+2 em+2 1 __ 2 (\"PH Demonstrate that this relation can be expressed as: _ (of 002 e Em w- _ (1)2 2 50 6 +2 and (of = wT 0+2 Ego where 2 2 007-:pr