Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Mass-density and Phonon-frequency Relaxation Dynamics of
  Under-coordinated Water Molecules   The interplay between intra-molecular H-O covalent bond contraction, due to
molecular under-coordination, and inter-molecular O:H expansion, due to
inter-electron pair Coulomb repulsion, has been shown to be the source of the
anomalous behavior of under-coordinated water molecules in nanoclusters and in
the surfaces of water. The shortening of the H-O bond raises the local density
of bonding electrons, which in turn polarizes the lone pairs of electrons on
oxygen. The stiffening of the H-O bond increases the magnitude of O1s binding
energy shift, causes the blueshift of the H-O phonon frequencies, and
furthermore, elevates the melting point of molecular clusters and ultrathin
films of water, which gives rise to their ice-like behavior at room
temperature. At the same time, the elongation of the entire O:H-O bond
polarizes and enlarges the under-coordinated H$_2$O molecules.

2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph