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,ωe,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 |N1−N2|,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 ScX (X=Ti–Zn) dimers [Gutsev, Bauschlicher, and Andrews, in Theoretical Prospects of Negative Ions, edited by J. Kalcher (Research Signpost, Trivandrum, 2002), pp. 43–60] allows one to construct “periodic” 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