Chalcopyrite (CuPeS(2)) is an antiferromagnetic semiconductor with unusual magnetic and electrical properties,: which are still not clearly understood. Neutron diffraction experiments reveal a phase transition at similar to 50 K, that has been attributed to an unexpected appearance of magnetic moments on Co ions, having a paramagnetic arrangement down to SO K and then ordering to an antiferromagnetic state at lower temperatures In this study we use DFT-based computational methods to investigate the electronic structure and magnetic properties of CuFeS2 in order to obtain a reliable source of information for the interpretation of the observed magnetic behavior, and in particular to shed some light on the magnetic behavior of copper atoms in this,compound. We have calculated the electronic structure of the ground and low-energy magnetically excited states and, deduced a set of exchange coupling constants that are used afterward-in classical Monte Carlo: simulations to obtain magnetic susceptibility data, Which compare successfully With our experimental results above 470 K. From our results it can be inferred that copper atoms remain in a diamagnetic State in this temperature range, although spin delocalization from neighboring iron atoms results in a non-negligible spin density on the copper, atoms at high temperatures.