Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Thermodynamics of hydrogen vacancies in MgH2 from first-principles
  calculations and grand-canonical statistical mechanics
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex