Stability of hyperlithiated borides

Structures and energetics of BLin (n = 4-8) clusters are predicted using th e SCF, MP2, and B3LYP methods with the 6-31G(d) basis set, including energy evaluations at G2MP2. Cohesive energies, defined as the enthalpies of the BLin --> B + Li-n reactions, and Li and Li-2 elimination reaction enthalpie s are also estimated at B3LYP. This level of theory predicts the boron cohe sive energy to increase up to the BLi6 cluster after which it levels off. A ll BLin systems are thermodynamically stable with respect to Li and Li-2 di ssociations; BLi4 has the largest reaction enthalpies. The energetics of th e hyperlithiated borides obtained with B3LYP/6-31G(d) are in reasonable agr eement with those at G2MP2 but less satisfactory than those of the smaller BLin (n =1-3) systems, Computations on BLi4 with multiconfigurational quasi degenerate perturbation theory indicate that the B3LYP/6-31G(d) energies ma y be more reliable for the larger BLin systems.