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arXiv · 1405.5520

Positional disorder in ammonia borane at ambient conditions

E. Welchman·P. Giannozzi·T. Thonhauser
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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.

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E. Welchman, P. Giannozzi, T. Thonhauser. 2014-05-21. Positional disorder in ammonia borane at ambient conditions. https://doi.org/10.1103/physrevb.89.180101

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