Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Understanding doping, vacancy, lattice stability and superconductivity
  in KxFe2-ySe2   Metal-intercalated iron selenides are a class of superconductors that have
received much attention but are less understood in comparison with their
FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the
real phase responsible for superconductivity, and lattice stability have been
addressed based on first-principles calculations. New insights into the
distinct features in terms of carrier doping have been revealed.

27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph