Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ab initio shallow acceptor levels in gallium nitride   Impurity levels and formation energies of acceptors in wurtzite GaN are
predicted ab initio. Be_Ga is found to be the shallow (thermal ionization
energy $\sim$ 0.06 eV); $Mg_{Ga}$ and $Zn_{Ga}$ are mid-deep acceptors (0.23 eV
and 0.33 eV respectively); $Ca_{Ga}$ and $Cd_{Ga}$ are deep acceptors
($\sim$0.65 eV); $Si_N$ is a midgap trap with high formation energy; finally,
contrary to recent claims, $C_N$ is a deep acceptor (0.65 eV). Interstitials
and heteroantisites are energetically not competitive with substitutional
incorporation.

34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol