Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Unoccupied Band Structure of NbSe2 by Very-Low-Energy Electron
  Diffraction: Experiment and Theory   A combined experimental and theoretical study of very-low-energy electron
diffraction at the (0001) surface of 2H-NbSe2 is presented. Electron
transmission spectra have been measured for energies up to 50 eV above the
Fermi level with k|| varying along the GammaK line of the Brillouin zone. Ab
initio calculations of the spectra have been performed with the extended linear
augmented plane wave k-p method. The experimental spectra are interpreted in
terms of three-dimensional one-electron band structure. Special attention is
paid to the quasi-particle lifetimes: by comparing the broadening of the
spectral structures in the experimental and calculated spectra the energy
dependence of the optical potential Vi is determined. A sharp increase of Vi at
20 eV is detected, which is associated with a plasmon peak in the
Im(-1/epsilon) function. Furthermore, the electron energy loss spectrum and the
reflectivity of NbSe2 are calculated ab initio and compared with optical
experiments. The obtained information on the dispersions and lifetimes of the
unoccupied states is important for photoemission studies of the 3D band
structure of the valence band.

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The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph