C v optical = contribution to the specific heat due to the optical branch, n = ?, kB = Boltzmann's constant, x = hωE/kBT, where ωE= frequency of optical branch, T = temperature
The Einstein equation gives the contribution of the optical branch to the specific heat capacity. The frequency of each optical branch is given a value ωE that does not depend on the wavelength.
Solid State Physics, J S Blakemore, CUP, 2nd edition, 1985
