We have characterized LiAlH4 and its dimer [LiAlH4](2) in vacuum and in solution using Hartree-Fock (HF), Moller-Plesset (MP2), and DFT electronic structure calculations coupled to the PCM solvation model. We found that the dimer is the most relevant species in vacuum but that a significant fraction of monomeric species may exist in solution. Monte Carlo simulations of isolated and solvated LiAlH4 have also been performed to investigate structural changes with temperature and solvation. The predominant species in both vacuum and solution simulations at 300 K was found to be the bidentate isomer, in agreement with the PCM calculations. (C) 2002 Elsevier Science B.V. All rights reserved.