Text: Virial Expansions and Perturbations
Consider the discrete energy levels of a quantum harmonic oscillator:
En=ho(n+1/2)
(3.1)
Now, consider adding an oscillating discrete perturbation scaled by a parameter a:
ΔE=aw
(3.2)
where n = 0, 1, 2, ..., h is the angular Planck constant and w is the oscillator frequency.
a) 4P) For which states is the perturbation the most important? What are the units of a?
b) 6P) Assuming that a < 1, show that the first order perturbation theory correction to the Helmholtz free energy for N non-interacting, distinguishable oscillators is given by:
F=Na(1-e^(-βh)) cos(ωt)
(3.3)
You may find the following formula useful:
(-1)^j cos(x) = ∑(j=0)^(∞) (2j)!
(3.4)
c) 8P) Derive the first order correction to E, the internal energy for the same system. You may find the following relation useful:
ΔE = ∫(0)^(β) a^2 kT^2 dt
(3.5)