Search results for "Clusters"
showing 10 items of 1274 documents
Effect of melting on ionization potential of sodium clusters
2003
The effect of melting transition on the ionization potential has been studied for sodium clusters with 40, 55, 142, and 147 atoms, using ab initio and classical molecular dynamics. Classical and ab initio simulations were performed to determine the ionization potential of Na142 and Na147 for solid, partly melted, and liquid structures. The results reveal no correlation between the vertical ionization potential and the degree of surface disorder, melting, or the total energy of the cluster obtained with the ab initio method. However, in the case of 40 and 55 atom clusters, the ionization potential seems to decrease when the cluster melts.
The influence of molecular properties of additives on the stability of polyethylene in high electric fields
2003
Results are presented of studies of some molecular properties, i.e., dipole moment, total polarizability, and electronic polarizability, of dihalide and diamine derivatives of phenylene, p,p'-bi-phenylene and carbazole, which are used as additives for physical modification of polyethylene. The diffusion coefficients of these substances from a polyethylene matrix were estimated, and the stability of modified polyethylene in high electric fields (50 Hz) was found. The mechanism of action of high-voltage stabilizers in polyethylene was verified. >
Fission barriers of doubly charged silver clusters
1999
The monomer evaporation energies and fission barriers of doubly charged silver cluster ions in the size range 9≤n≤25 are measured by collision induced dissociation. They are compared to the dissociation energies of singly charged silver clusters. A macroscopic liquid drop model combined with empirical microscopic corrections successfully describes the measured fission barriers.
Self-Assembled Zinc Oxide Quantum Dots Using Spray Pyrolysis Methodology
2011
Self-assembled ZnO quantum dots (QDs) have been obtained on different substrates by using the atmospheric spray pyrolysis methodology under well-defined growth conditions. The evolution of size and...
Luminescence Center Excited State Absorption in Calcium and Zinc Tungsates
2002
The tungstate crystals are well known scintillators. The mechanism of luminescence center formation and the luminescence center model are under discussion today. The results of time-resolved spectroscopy of luminescence center in ZnWO4 and CaWO4 in wide temperature regions was presented. The luminescence and induced absorption under pulsed electron beam excitation (pulse duration 10 ns, 0.26 MeV) were studied. The experimental equipment used allows one to obtain the transient absorption spectra, luminescence decay kinetics and transient absorption relaxation times.
First-principles calculations of perovskite thin films
2002
Abstract The results of the electronic structure calculations for different surface terminations of SrTiO3 (1 0 0) perovskite thin films are discussed. These calculations are based on ab initio Hartree–Fock method with a posteriori electron correlation corrections and density functional theory with a number of different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Results are compared with previous ab initio plane-wave local density approximation and classical shell model calculations. Calculated considerable increase of the Ti–O chemical bond covalency nearby the surface is confirmed by experimental data. We predict also the band-gap reduction, espe…
Electronic Shell Structure and the Crystal Field Splitting in Simple Metals Clusters
1991
An upper limit for the number of atoms in metal clusters capable of exhibiting electronic shell structure has been estimated by comparing the energy difference between the highest occupied and the lowest unoccupied state with the crystal field splitting. The former is obtained by solving the Schrodinger equation for a spherical potential well with hard walls while the latter is obtained from the band structure of the solid. The results indicate that shell structures may persist in clusters containing as many as a million atoms.
Neutron scattering study of structural and magnetic size effects in NiO
2013
Nickel oxide powders with the grain size of 13–1500 nm have been studied by neutron scattering, scanning electron microscopy and vibrating sample magnetometry. We have found that the atomic structure and the antiferromagnetic ordering are nearly independent of the average size of grains. The existence of the uncompensated spins in nanoparticles with the grain size below 100 nm has been detected.
Multiwall carbon-nanotube interconnects: radial effects on physical models and resistance calculations for various metal substrates
2010
Based on a model with singular attractive potential of equidistant conductive cylinders, we illustrate an approach to calculate the electron spectrum of metallic multiwall carbon nanotubes (MW CNT) with an arbitrary number of coaxial layers. We compute the number of electrically active channels, N ch , in the ideal case when all MW CNT shells are contacted to the electrodes, starting from the one-electron spectrum. The dependence of N ch on the temperature and on both the innermost and outermost shells radii allows us to discuss the potential performances of MW CNT interconnects, affecting the power dissipation of integrated circuits. Our description improves over the isolated shells model,…
DFT calculations on subnanometric metal catalysts: a short review on new supported materials
2018
Metal clusters have been used in catalysis for a long time, even in industrial production protocols, and a large number of theoretical and experimental studies aimed at characterizing their structure and reactivity, either when supported or not, are already present in the literature. Nevertheless, in the last years the advances made in the control of the synthesis and stabilization of subnanometric clusters promoted a renewed interest in the field. The shape and size of sub-nanometer clusters are crucial in determining their catalytic activity and selectivity. Moreover, if supported, subnanometric clusters could be highly influenced by the interactions with the support that could affect geo…