  First-principles, density-functional based electronic structure calculations
are carried out for MgC(Ni_{1-x}Co_{x})_{3} alloys over the concentration range
0\leq x\leq1, using Korringa-Kohn-Rostoker coherent-potential approximation
(KKR CPA) method in the atomic sphere approximation (ASA). The self-consistent
calculations are used to study the changes as a function of x in the equation
of state parameters, total and partial densities of states, magnetic moment and
the on-site exchange interaction parameter. To study the magnetic properties as
well as its volume dependence, fixed-spin moment calculations in conjunction
with the phenomenological Landau theory are employed. The salient features that
emerge from these calculations are (i) a concentration independent variation in
the lattice parameter and bulk modulus at x~0.75 with an anomaly in the
variation of the pressure derivative of bulk modulus, (ii) the fixed-spin
moment based corrections to the overestimated magnetic ground state for 0.0\leq
x\leq0.3 alloys, making the results consistent with the experiments, and (iii)
the possibility of multiple magnetic states at x~0.75, which, however, requires
further improvements in the calculations.
