Electronic structure and magnetic properties of CoS_2 with a cubic-pyrite-type structure have been studied by a first-principles density functional theory (DFT) calculation using a linear muffin-tin orbital method within the framework of the generalized gradient approximation for the treatment of exchange-correlation effects. The total energy and magnetic moments are calculated as a function of lattice constant. The calculated lattice constant and magnetic moments are in good agreement with the experimental results. The pressure-volume relationship is obtained by fitting the calculated total energy to the universal equation of state. The derived bulk modulus is 137 GPa and the equilibrium volume is 42.16 A~3/f.u. The calculated Co magnetic moment decreases at a rate of -0.0055 μ_B/GPa as the external pressure less than 3.6 GPa, in agreement with the experimental value of -0.005 μ_B/GPa. The DFT calculations predict the occurrence of a first order pressure induced magnetic transition in CoS_2 at a high pressure (12 GPa), which is qualitatively consistent with the experimental data which show that the ferromagnetic state in CoS_2 is unstable at external pressures higher than 6 GPa.
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