  We present ab initio studies of structures, energetics, and diffusion
properties of Mg in Si, Ge, and Sn diamond structures to evaluate their
potential as insertion type anode materials for Mg batteries. We show that Si
could provide the highest specific capacities (3817 mAh g-1) and the lowest
average insertion voltage (~0.15 eV vs. Mg) for Mg storage. Nevertheless, due
to its significant percent lattice expansion (~216%) and slow Mg diffusion, Sn
and Ge are more attractive; both anodes have lower lattice expansions (~120 %
and ~178 %, respectively) and diffusion barriers (~0.50 and ~0.70 eV,
respectively for single-Mg diffusion) than Si. We show that Mg-Mg interactions
at different stages of charging can decrease significantly the diffusion
barrier compared to the single atom diffusion, by up to 0.55 eV.
