Positional disorder in ammonia borane at ambient conditions

Abstract

We solve a long-standing experimental discrepancy of NH${}_3$BH${}_3$, which---as a molecule---has a threefold rotational axis, but in its crystallized form at room temperature shows a fourfold symmetry about the same axis, creating a geometric incompatibility. To explain this peculiar experimental result, we study the dynamics of this system with ab initio Car-Parrinello molecular dynamics and nudged-elastic-band simulations. We find that rotations, rather than spatial static disorder, at angular velocities of 2 rev/ps---a time scale too small to be resolved by standard experimental techniques---are responsible for the fourfold symmetry.

References in corpus (4)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Van der Waals Density Functional for General Geometries
• Van der Waals density functional: Self-consistent potential and the nature of the van der Waals bond
• High-pressure phase and transition phenomena in ammonia borane NH3BH3 from X-ray diffraction, Landau theory, and ab initio calculations

Cited by in corpus (1)

• Lowering the hydrogen desorption temperature of NH3BH3 through B-group substitutions