Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A theoretical study of the hydrogen-storage potential of (H_2)_4CH_4 in
  metal organic framework materials and carbon nanotubes   The hydrogen-methane compound (H_2)_4CH_4---or for short H4M---is one of the
most promising hydrogen-storage materials. This van der Waals compound is
extremely rich in molecular hydrogen: 33.3 mass%, not including the hydrogen
bound in CH_4; including it, we reach even 50.2 mass%. Unfortunately, H4M is
not stable under ambient pressure and temperature, requiring either low
temperature or high pressure. In this paper, we investigate the properties and
structure of the molecular and crystalline forms of H4M, using ab initio
methods based on van der Waals DFT (vdW-DF). We further investigate the
possibility of creating the pressures required to stabilize H4M through
external agents such as metal organic framework (MOF) materials and carbon
nanotubes, with very encouraging results. In particular, we find that certain
MOFs can create considerable pressure for H4M in their cavities, but not enough
to stabilize it at room temperature, and moderate cooling is still necessary.
On the other hand, we find that all investigated carbon nanotubes can create
the high pressures required for H4M to be stable at room temperature, with
direct implications for new and exciting hydrogen-storage applications.

27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph