The development of high energy density and high efficiency hydrogen storage materials is widely considered to be one of the most challenging barriers to the adoption of fuel cell power trains in transportation applications. Magnesium forms a high hydrogen gravimetric density (14.9wt%) tetrahydroborate (Mg(BH4)2) with a relatively low decomposition temperature (Tdec ~ 300C). We have identified and obtained a structural solution for a new low temperature cubic polymorph of Mg(BH4)2. Furthermore, we have identified a novel transformation process with 2 further, novel, polymorphs. We wish to study these 3 new polymorphs and the amorphous product of decomposition using TOSCA. These studies will provide information on the behaviour and environment of the tetrahydroborate anion as a function of structure and allow us to deteme the mechanisms of phase transformation and decomposition.