Effects of Dispersion Corrections and Nonlocality on Density Functional Predictions of Pressure-Induced Polymorphic Transitions of Crystalline Diborane

Abstract

The role of dispersion interactions in density functional calculations of the relative enthalpies of compressed BH3 polymorphs was investigated using plane-wave and Gaussian basis set codes. Addition of semiempirical atom-pairwise dispersion corrections to generalized gradient approximations (GGAs) was found to have little effect on the relative enthalpies of various boron hydride structures. By contrast, the stability ranking obtained with the nonlocal van der Waals density functional (vdW-DF) of Dion and co-workers was substantially more realistic than the rankings predicted by plain and dispersion-corrected GGAs. Of the functionals tested, only vdW-DF correctly predicts that compressed diborane does not leave the B2H6 motif until at least 20 GPa. This finding serves as direct computational evidence of the thermodynamic stability of molecular B2H6 units in the 0–20 GPa pressure range, an experimental result that until now has been at variance with theoretical predictions.