Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Free-electron effects on optical absorption of hybrid perovskite
  CH$_3$NH$_3$PbI$_3$ from first principles
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th