Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Positional disorder in ammonia borane at ambient conditions   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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The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess