7 research outputs found
Systematic Study of Electron Localization in an Amorphous Semiconductor
We investigate the electronic structure of gap and band tail states in
amorphous silicon. Starting with two 216-atom models of amorphous silicon with
defect concentration close to the experiments, we systematically study the
dependence of electron localization on basis set, density functional and spin
polarization using the first principles density functional code Siesta. We
briefly compare three different schemes for characterizing localization:
information entropy, inverse participation ratio and spatial variance. Our
results show that to accurately describe defect structures within self
consistent density functional theory, a rich basis set is necessary. Our study
revealed that the localization of the wave function associated with the defect
states decreases with larger basis sets and there is some enhancement of
localization from GGA relative to LDA. Spin localization results obtained via
LSDA calculations, are in reasonable agreement with experiment and with
previous LSDA calculations on a-Si:H models.Comment: 16 pages, 11 Postscript figures, To appear in Phys. Rev.
All-electron magnetic response with pseudopotentials: NMR chemical shifts
A theory for the ab initio calculation of all-electron NMR chemical shifts in
insulators using pseudopotentials is presented. It is formulated for both
finite and infinitely periodic systems and is based on an extension to the
Projector Augmented Wave approach of Bloechl [P. E. Bloechl, Phys. Rev. B 50,
17953 (1994)] and the method of Mauri et al [F. Mauri, B.G. Pfrommer, and S.G.
Louie, Phys. Rev. Lett. 77, 5300 (1996)]. The theory is successfully validated
for molecules by comparison with a selection of quantum chemical results, and
in periodic systems by comparison with plane-wave all-electron results for
diamond.Comment: 25 pages, 4 tables, submitted to Physical Review
First-principles investigation of electronic structure and optical properties in N-F codoped ZnO with wurtzite structure
The electronic structures and optical properties of pure, N-doped and N-F codoped ZnO are investigated based on the density-functional theory. The calculations of the impurity formation energies and ionization energies for these systems indicate that incorporating the reactive donor F into N doped ZnO systems, not only enhances the N acceptor solubility, but also leads to a shallower N acceptor energy level in the band gap in p-type codoped ZnO. In addition, we analyze the imaginary part of the dielectric functions, and reflectivities for pure and N-F codoped ZnO. Compared with the pure ZnO, the remarkable feature in the dielectric function for N-F codoped ZnO is that there is a sharp peak in the low-energy region. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011