Search results for "clusters"
showing 10 items of 1274 documents
A Comparative Ab Initio Thermodynamic Study of Oxygen Vacancies in ZnO and SrTiO3: Emphasis on Phonon Contribution
2013
Using a hybrid Hartree–Fock (HF)-DFT method combined with LCAO basis set and periodic supercell approach, the atomic, electronic structure and phonon properties of oxygen vacancies in ZnO and SrTiO3 were calculated and compared. The important role of a ghost basis function centered at the vacant site and defect spin state for SrTiO3 is discussed. It is shown that the use of hybrid functionals is vital for correct reproduction of defects basic properties. The Gibbs free energy of formation of oxygen vacancies and their considerable temperature dependence has been compared for the two oxides. These calculations were based on the polarizability model for the soft mode temperature behavior in S…
Electrical fluctuations in monolayer-protected metal nanoclusters
2008
Abstract Monolayer-protected clusters (MPCs) are formed by a neutral or charged metallic core surrounded by an organic ligand monolayer. We estimate the electric potential fluctuations of a MPC in an electrolyte solution by using the equilibrium fluctuation–dissipation theorem and the non-linear Poisson–Boltzmann equation extended to account for ion penetration in the monolayer. Significant fluctuations are predicted because the MPC capacitance is small (approximately 1 aF). We study also the non-equilibrium case of a MPC sandwiched between two electrodes and estimate the current noise considering the nanocluster as a single electron transistor and using a theoretical approach based on the …
Ab initio Hartree-Fock calculations of LaMnO3 (110) surfaces
2003
We present the results of ab initio Hartree-Fock calculations of the LaMnO3 (110) surface. Using seven-plane slabs, periodic in 2D and containing three formula units, we compare the properties of a stoichiometric surface with oxygen vacancies, and non-stoichiometric, defect-free surfaces, analyze the dispersion of the effective charges near the surface, and calculate the surface energy before and after relaxation, for both ferromagnetric and antiferromagnetic spin orderings in a slab. q 2003 Elsevier Ltd. All rights reserved.
Calculations of the atomic and electronic structure for SrTiO3 perovskite thin films
2001
The results of calculations of SrTiO3 (100) surface relaxation and rumpling with two different terminations (SrO and TiO2) are presented and discussed. We have used the ab initio Hartree–Fock (HF) method with electron correlation corrections and the density functional theory (DFT) with different exchange–correlation functionals, including hybrid exchange techniques. All methods agree well on surface energies and on atomic displacements, as well as on the considerable increase of covalency effects near the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing of theoretical predictions.
DFT plane wave calculations of the atomic and electronic structure of LaMnO3(001) surface
2009
We present the results of ab initio DFT plane wave periodic structure calculations of the LaMnO3 (001) surface. The effects related to three different kinds of pseudopotentials, the slab thickness, magnetic ordering, and surface relaxation are studied and discussed. The antiferromagnetic surface lowest in energy (that is, the spins on Mn ions are parallel in basal plane and antiparallel from plane to plane) has a considerable atomic relaxation up to the fourth plane from the surface. The calculated (Bader) effective charges and the electronic density maps demonstrate a considerable reduction of the Mn atom ionicity on the surface accompanied by a covalent contribution to the Mn–O bonding.
Syntheses, Structures, Magnetic Properties, and Density Functional Theory Magneto-Structural Correlations of Bis(μ-phenoxo) and Bis(μ-phenoxo)-μ-acet…
2013
The bis(mu-phenoxo) (FeNiIII)-Ni-II compound [Fe-III(N-3)(2)LNiII(H2O)(CH3CN)](ClO4) (1) and the bis(mu-phenoxo)-mu-acetate/bis(mu-phenoxo)-bis(mu-acetate) (FeNiII)-Ni-III compound {[Fe-III(OAc)LNiII(H2O)(mu-OAc)](0.6)center dot[(FeLNiII)-L-III(mu-OAc)(2)](0.4)}(ClO4)center dot 1.1H(2)O (2) have been synthesized from the Robson type tetraiminodiphenol macrocyclic ligand H2L, which is the [2 + 2] condensation product of 4-methyl-2,6-diformylphenol and 2,2'-dimethy1-1,3-diaminopropane. Single-crystal X-ray structures of both compounds have been determined. The cationic part of the dinuclear compound 2 is a cocrystal of the two species [Fe-III(OAc)LNiII(H2O)(mu-OAc)](+) (2A) and [(FeLNiII)-L-I…
An Na8 Cluster in the Structure of a Novel oxamato-bridged Na'Cu'' three-Dimensional Coordination Polymer
1999
[EN] The new heterometallic sodium(I)¿copper(II) compound Na4Cu2 (2) · 10.5 H2O (3), where H8[2] stands for N,N',N'',N'''-methanetetrayltetrakismethylenetetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of cationic [Cu2(¿4:¿4-2)]4- dinuclear units, coordinated sodium cations, and water molecules. In the crystal, the dinuclear copper entities are joined through discrete aggregates of eight sodium atoms linked by oxamato and water bridges, leading to a three-dimensional polymeric network.
Europe 2020 Strategy and New Policies for Marginal Areas
2014
Marginality should be seen as an a asset rather than a liability for a region or a community. Marginality reflects a strategy of economic development, and this paper also seeks institutional means for championing marginality over conformity.
Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping
2015
By means of zoom-in hydrodynamic simulations we quantify the amount of neutral hydrogen (HI) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics (SPH), include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split in two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analyzed to account for HI self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter halos monotonically increases with the halo mass and can be well described by a power-law of th…
Pressure of the hot gas in simulations of galaxy clusters
2016
We analyze the radial pressure profiles, the ICM clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the TreePM-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, AGN and/or stellar feedback. Our results are analyzed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observa…