Quasiharmonic EOS quasiharmonic

cold_curve (see below)
number_of_kinetic_modes_per_molecule
For each:
   w(v) dw(v)/dv d2w(v)/dv2   degeneracy
molecular_mass
hbar kBoltzmann

Notes:

• Cold curves are also polymorphic objects, described separately..
• Each function of w (angular frequency) is a WXMATHS Realfunction1d * object.
• Angular frequencies, mass and the physical constants must be specified in units consistent with the calculation.