Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theoretical evidences for enhanced superconducting transition
  temperature of CaSi$_2$ in a high-pressure AlB$_2$ phase   By means of first-principles calculations, we studied stable lattice
structures and estimated superconducting transition temperature of CaSi$_2$ at
high pressure. Our simulation showed stability of the AlB$_2$ structure in a
pressure range above 17 GPa. In this structure, doubly degenerated optical
phonon modes, in which the neighboring silicon atoms oscillate alternately in a
silicon plane, show prominently strong interaction with the conduction
electrons. In addition there exists a softened optical mode (out-of-plan motion
of silicon atoms), whose strength of the electron-phonon interaction is nearly
the same as the above mode. The density of states at the Fermi level in the
AlB$_2$ structure is higher than that in the trigonal structure. These findings
and the estimation of the transition temperature strongly suggest that higher
$T_{\rm c}$ is expected in the AlB$_2$ structure than the trigonal structures
which are known so far.

20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc