[摘要]：The structural property of crystalline ammonia borane NH3BH3 is studied by means of density-functional theory calculations. The prototypical inter-molecular N-H center dot center dot center dot H-B dihydrogen bonds are found to be weak so as to make the crystal structure flexible and sensitive to the calculational methods. We found that although conventional generalized gradient approximation describes the intra-molecular bonding in ammonia borane reasonably well, it predicts too large unit cell volume and wrong lattice parameters. Inclusion of the van der Waals forces through the semi-empirical correction improves the cell parameters and inter-molecular geometry significantly, suggesting the important role of van der Waals forces in the bonding between ammonia borane molecules. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657526]
