Quantum Monte Carlo calculations of the dimerization energy of borane

Accurate thermodynamic data are required to improve the performance of chemical hydrides that are potential hydrogen storage materials. Boron compounds are among the most interesting candidates.
However, different experimental measurements of the borane dimerization energy resulted in a rather wide range (−34.3 to −39.1) ± 2 kcal/mol. Diffusion Monte Carlo (DMC) simulations usually recover more than 95% of the correlation energy, so energy differences rely less on error cancellation than other methods. DMC energies of BH3, B2H6, BH3 CO, CO, and BH2+ allowed us to predict the borane dimerization energy, both via the direct process and indirect processes such as the dissociation of BH3CO. Our De = −43.12(8) kcal/mol, corrected for the zero point energy evaluated by considering the anharmonic contributions, results in a borane dimerization energy of −36.59(8) kcal/mol. The process via the dissociation of BH3CO gives −34.5(2) kcal/mol. Overall, our values suggest a slightly less De than the most recent W4 estimate De =−44.47 kcal/mol [A. Karton and J. M. L. Martin, J. Phys. Chem. A 111, 5936 2007)]. Our results show that reliable thermochemical data for boranes can be predicted by fixed node (FN)-DMC calculations.