Calculating the physical properties of isotopes
The Debye frequency of a crystal is a theoretical maximum frequency of vibration for the atoms that make up the crystal. 


It seems safe to assume melting will be occurring at the Debye frequency. 

It is quite possible that the authors of your paper used the Lindemann model, which was published in 1910, in conjunction with Debye frequency, which is unique to each topoisomer, to predict the melting point using the following equation of Lindemann: 

$$ T_m = \cfrac{4\pi^2 m \nu^2 c^2 a^2}{k_B} $$

$$m = \mathrm{atomic\ mass}$$ $$ v = \mathrm{frequency} $$   $$ k_B=\mathrm{Boltzmann\ constant}$$ $$T=\mathrm{temperature}\ \left(^\circ \mathrm K\right)$$ $$c = \mathrm{Lindemann\ constant}$$   $$a = \mathrm{atomic\ spacing}$$

Different diastereomers have different resonant frequencies which can be found through either Debye calculations or IR and Raman spectroscopy.

Substituting in the Debye expression for frequency (I copied this from Wikipedia; I didn't actually derive it myself) gives:

$$ T_m = \cfrac{2\pi m (\theta^2_D k_B)c^2 a^2}{\hbar^2} $$

Where $\theta^2_D$ is the Debye temperature and $\hbar$ is Planck's constant.  

Another way of doing it is by using a hard sphere model in combination with Debye/Lindemann (PDF link).