Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Formation and migration of native defects in NaAlH$_4$   We present a first-principles study of native defects in NaAlH$_4$. Our
analysis indicates that the structure and energetics of these defects can be
interpreted in terms of elementary building blocks, which include
$V_{\rm{AlH_4}}^+$, $V_{\rm{Na}}^-$, $V_{\rm{H}}^+$, H$_i^-$, and (H$_2$)$_i$.
We also calculate migration barriers for several key defects, in order to
compare enthalpies of diffusion to experimentally measured activation energies
of desorption. From this, we estimate activation energies for diffusion of
defects and defect pairs. We suggest that $V_{\rm{AlH_4}}^+$ and H$_i^-$, or
$V_{\rm{Na}}^-$ and $V_{\rm{H}}^+$, may be responsible for diffusion necessary
for desorption. We discuss the possible role of $V_{\rm{H}}^+$-H$_i^-$ complex
formation. The values we find are in the range of activation energies reported
for catalyzed desorption.

31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
1
The categories of this paper are: cs
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
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The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas