Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electronic structure and excitations in oxygen deficient
  CeO$_{2-\delta}$ from DFT calculations   The electronic structures of supercells of CeO$_{2-\delta}$ have been
calculated within the Density Functional Theory (DFT). The equilibrium
properties such as lattice constants, bulk moduli and magnetic moments are well
reproduced by the generalized gradient approximation (GGA). Electronic
excitations are simulated by robust total energy calculations for constrained
states with atomic core- or valence-holes. Pristine ceria CeO$_2$ is found to
be a non-magnetic insulator with magnetism setting in as soon as oxygens are
removed from the structure. In the ground state of defective ceria, the Ce-$f$
majority band resides near the Fermi level, but appears at about 2 eV below the
Fermi level in photoemission spectroscopy experiments due to final state
effects. We also tested our computational method by calculating threshold
energies in Ce-M$_5$ and O-K x-ray absorption spectroscopy and comparing
theoretical predictions with the corresponding measurements. Our result that
$f$ electrons reside near the Fermi level in the ground state of oxygen
deficient ceria is crucial for understanding catalytic properties of CeO$_2$
and related materials.

8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an