Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Physical properties of ReB2 under high pressure and effect of metallic
  bonding on its hardness   Using first-principles calculations, the elastic constants, thermodynamic
property and structural phase transition of rhenium diboride under pressure are
investigated by means of the pseudopotential plane-waves method, as well as the
effect of metallic bond on its hardness. Eight candidate structures of known
transition-metal compounds are chosen to probe for rhenium diboride ReB2. The
calculated lattice parameters are consistent with the experimental and
theoretical values. Based on the third order equation of states, the transition
pressure Pt between the ReB2-ReB2 and MoB2-ReB2 phases is firstly determinate.
Elastic constants, shear modulus, modulus, ratio and temperature are derived.
The single-bonded feather remains in ReB2 compounds.Furthermore, a
semiempirical method to evaluate the hardness of multicomponent crystals with
partial metallic bond is presented. The effect of metallic bond on the hardness
of ReB2 is searched and the hardness shows a gradual increase under
compression, which is different from diamond.

10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th