Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Confinement effects in ultra-thin ZnO polymorph films: electronic and
  optical properties   Relying on generalized-gradient and hybrid first-principles simulations, this
work provides a complete characterization of the electronic properties of ZnO
ultra-thin films, cut along the Body-Centered-Tetragonal(010), Cubane(100),
h-BN(0001), Zinc-Blende(110), Wurtzite(10$\bar{1}$0) and (0001) orientations.
The characteristics of the local densities of states are analyzed in terms of
the reduction of the Madelung potential on under-coordinated atoms and surface
states/resonances appearing at the top of the VB and bottom of the CB. The gap
width in the films is found to be larger than in the corresponding bulks, which
is assigned to quantum confinement effects. The components of the high
frequency dielectric constant are determined and the absorption spectra of the
films are computed. They display specific features just above the absorption
threshold due to transitions from or to the surface resonances. This study
provides a first understanding of finite size effects on the electronic
properties of ZnO thin films and a benchmark which is expected to foster
experimental characterization of ultra-thin films via spectroscopic techniques.

30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio