It is thought that matter in white dwarf cores and neutron star crusts is arranged in the body-centered cubic (bcc) Coulomb lattice. In this work we consider thermodynamic properties of bcc lattice with isotopic impurities using a modified perturbation theory of spectra of disordered crystal. We compare our results with those obtained using the linear mixing theory. It is shown that both methods give similar results when the mass of the impurities is not much different from the weight of the basic ions but a significant discrepancy is observed when impurities are much lighter or heavier.

Page created on September 6, 2013.