Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comments on the momentum density and the spatial form of the
  density-matrix of the Hooke's atom   In a recent paper, A. Akbari, N. H. March and A. Rubio [Phys. Rev. A. 76,
032510 (2007)] have investigated the one-electron reduced density-matrix and
the momentum density of several two-electron model atoms, including the Hooke's
atom. The method used by the authors for deriving an integral form of the
momentum density is well suited for deriving a closed-form expression of the
exact reciprocal form factor, which function is of importance inasmuch as it
reflects the off-diagonal side of the exact reduced density-matrix.

32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
23
The categories of this paper are: solv-int