MgCl2 is a support of choice for industrial production of polyolefins in Ziegler-Natta catalysis. Recent experiments have shown that the inert (001) MgCl2 surface can be activated by electron irradiation. To better understand this process, we have studied the properties of point defects on the (001) surface and their interaction with TiCl4. We have used density functional theory and Car-Parrinello methods and calculated mono- and di-vacancies of Cl and Cl-. Particularly interesting is the case of Cl di-vacancy which is heavily reconstructed and forms with TiCl4 a structure where the Ti atom is bounded with a Mg atom.