density functional theory (DFT).
To define the entropy of a Cu–Zn system without any structural
changes, the entropy difference between a hypothetical fcc-Zn and
the hcp-Zn structure has to be calculated. Therefore, lattice
dynamics calculations using the DFT plane wave pseudopotential
approach of both structures were performed. The resulting dispersion
relations are compared in figure 5. The mean frequency of the
fcc-structure is lower compared to that of the hcp-structure and it
seems that the absence of different crystallographic sites and in
consequence the absence of the optical modes in the fcc-structure
is responsible for this shift.