9 research outputs found
A DFT + U Study of Absorption Spectra and Localized Surface Plasmon Resonances of few electrons in Doped ZnO Quantum Dots
Quantum plasmonics of few electrons that was reported a few years ago in
photodoping experiments has received little or no attention in doped
nanomaterials both theoretically and experimentally. There are no studies of
quantum plasmonics of large quantum dots of the size of Bohr excitonic radius
or less that take electronic and geometric structure of the quantum dots. In
this work, we studied extensively the absorption spectra of a protype quantum
dot of sizeable ZnO of approximately 3.0 nm in diameter doped with Ga, and Al
in diluted limit with density functional theory (DFT) plus Hubbard corrections
(U). The localized surface plasmon resonances (LSPRs) were then determined from
the real part of the dielectric function by correlating the negative portion of
it to resonant spectral lines. Our results show the sensitivity of the spectral
lines to distribution of the dopants, the electronic structure of the dopants,
the polarization of the electric field, and size of the quantum dots. Even
though our findings are based on stoichiometrically simple ZnO, it shows that
the DFT + U method with numerical atomic basis can be used at reasonable
computational cost to study quantum plasmonics of few electrons taking into
account electronic and geometric structures, which is missing currently. The
method can be extended to study magneto-optics of diluted magnetic
semiconductor QDs.Comment: 21 pages, 11 figure
Periodic table of 3d-metal dimers and their ions
The ground states of the mixed 3d-metal dimers TiV, TiCr, TiMn, TiFe, TiCo, TiNi, TiCu, TiZn, VCr, VMn, VFe, VCo, VNi, VCu, VZn, CrMn, CrFe, CrCo, CrNi, CrCu, CrZn, MnFe, MnCo, MnNi, MnCu, MnZn, FeCo, FeNi, FeCu, FeZn, CoNi, CoCu, CoZn, NiCu, NiZn, and CuZn along with their singly negatively and positively charged ions are assigned based on the results of computations using density functional theory with generalized gradient approximation for the exchange-correlation functional. Except for TiCo and CrMn, our assignment agrees with experiment. Computed spectroscopic constants (re,Ïe,Do) are in fair agreement with experiment. The ground-state spin multiplicities of all the ions are found to differ from the spin multiplicities of the corresponding neutral parents by ±1. Except for TiV, MnFe, and MnCu, the number of unpaired electrons, N, in a neutral ground-state dimer is either N1+N2 or |N1âN2|,where N1 and N2 are the numbers of unpaired 3d electrons in the 3dn4s1 occupation of the constituent atoms. Combining the present and previous results obtained at the same level of theory for homonuclear [Gutsev and Bauschlicher, J. Phys. Chem. A 107, 4755 (2003)] 3d-metal and ScXâ(X=TiâZn) dimers [Gutsev, Bauschlicher, and Andrews, in Theoretical Prospects of Negative Ions, edited by J. Kalcher (Research Signpost, Trivandrum, 2002), pp. 43â60] allows one to construct âperiodicâ tables of all 3d-metal dimers along with their singly charged ions
Broken-symmetry-adapted Green function theory of condensed matter systems:towards a vector spin-density-functional theory
The group theory framework developed by Fukutome for a systematic analysis of
the various broken symmetry types of Hartree-Fock solutions exhibiting spin
structures is here extended to the general many body context using spinor-Green
function formalism for describing magnetic systems. Consequences of this theory
are discussed for examining the magnetism of itinerant electrons in nanometric
systems of current interest as well as bulk systems where a vector spin-density
form is required, by specializing our work to spin-density-functional
formalism. We also formulate the linear response theory for such a system and
compare and contrast them with the recent results obtained for localized
electron systems. The various phenomenological treatments of itinerant magnetic
systems are here unified in this group-theoretical description.Comment: 17 page
Non-ergodic effects in the Coulomb glass: specific heat
We present a numerical method for the investigation of non-ergodic effects in
the Coulomb glass. For that, an almost complete set of low-energy many-particle
states is obtained by a new algorithm. The dynamics of the sample is mapped to
the graph formed by the relevant transitions between these states, that means
by transitions with rates larger than the inverse of the duration of the
measurement. The formation of isolated clusters in the graph indicates
non-ergodicity. We analyze the connectivity of this graph in dependence on
temperature, duration of measurement, degree of disorder, and dimensionality,
studying how non-ergodicity is reflected in the specific heat.Comment: Submited Phys. Rev.
Universal Crossover between Efros-Shklovskii and Mott Variable-Range-Hopping Regimes
A universal scaling function, describing the crossover between the Mott and
the Efros-Shklovskii hopping regimes, is derived, using the percolation picture
of transport in strongly localized systems. This function is agrees very well
with experimental data. Quantitative comparison with experiment allows for the
possible determination of the role played by polarons in the transport.Comment: 7 pages + 1 figure, Revte
Manganese nanoclusters and nanowires on GaAs surfaces
We have computed the local magnetic moments of manganese and neighboring
arsenic for various cluster configurations on the (001) surface of GaAs bulk
crystal using a cluster of 512 atoms. We obtained for manganese a substantial
local magnetic moment of 3.66 Bohr magnetons for all cases considered. The
induced magnetic moment of arsenic is less than that of manganese by two orders
of magnitude and falls off drastically beyond nearest neighbor distance. A
small amount of charge is transferred from the manganese to arsenic. The
possibility of a spin polarized wire channel on the arsenic layer below the
surface is suggested.Comment: 17 pages (includes 2 tables and 3 figures