As far as thermodynamics is concerned, choosing this common value as zero is a
matter of convenience. The molecular interpretation of entropy, however, justifies
the value S = 0 at T = 0. We saw in Section 3.2b that, according to the Boltzmann
formula, the entropy is zero if there is only one accessible microstate (W = 1). In most
cases, W = 1 at T = 0 because there is only one way of achieving the lowest total energy:
put all the molecules into the same, lowest state. Therefore, S = 0 at T = 0, in accord
with the Third Law of thermodynamics. In certain cases, though, W may differ from
1 at T = 0. This is the case if there is no energy advantage in adopting a particular
orientation even at absolute zero. For instance, for a diatomic molecule AB there may