  First-principles, density-functional-based electronic structure calculations
are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3}
and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential
approximation method in the atomic sphere approximation (KKR-ASA CPA). As a
function of decreasing C at%, we find a steady decrease in the lattice constant
and bulk modulus in either alloys. However, the pressure derivative of the bulk
modulus displays an opposite trend. Following the Debye model, which relates
the pressure derivative of the bulk modulus with the average phonon frequency
of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys
posses a different phonon spectra in comparison to its MgCNi_{3} counterparts.
This is further justified by the marked similarity we find in the electronic
structure properties such as the variation in the density of states and the
Hopfield parameters calculated for these alloys. The effects on the equation of
state parameters and the density of states at the Fermi energy, for partial
replacement of Mg by Zn are also discussed.
