Search results for " Clusters"
showing 10 items of 1091 documents
Shell structure in mixed3He−4Hedroplets
2004
Due to the immiscibility of ${}^{3}\mathrm{He}$ into ${}^{4}\mathrm{He}$ at very low temperatures, mixed helium droplets consist of a core of ${}^{4}\mathrm{He}$ atoms coated by a ${}^{3}\mathrm{He}$ layer whose thickness depends on the number of atoms of each isotope. When these numbers are such that the centrifugal kinetic energy of the ${}^{3}\mathrm{He}$ atoms is small and can be considered as a perturbation to the mean-field energy, a novel shell structure arises, with magic numbers different from these of pure ${}^{3}\mathrm{He}$ droplets. If the outermost shell is not completely filled, the valence atoms align their spins up to the maximum value allowed by the Pauli principle.
Quantum chemical simulations of hole self-trapping in semi-ionic crystals
1994
A novel formalism is presented for reliable calculations of the energetics of hole self-trapping in semi-ionic solids with mixed valence bands. Unlike previous model-Hamiltonian-type approaches, it is based on self-consistent quantum chemical INDO simulations of the atomistic and electronic structure of a self-trapped hole, making no a priori assumptions about a particular form of its localization (if any). This formalism is applied to the problem of hole self-trapping in corundum crystals (a -A1203). The hole self-trapping is found to be energetically favorable in the form of a diatomic 02 molecule with strong covalent bonding quite similar to the self-trapped hole (VK-center) in alkali ha…
Confined Pt-1(1+) Water Clusters in a MOF Catalyze the Low-Temperature Water-Gas Shift Reaction with both CO2 Oxygen Atoms Coming from Water
2018
[EN] The synthesis and reactivity of single metal atoms in a low-valence state bound to just water, rather than to organic ligands or surfaces, is a major experimental challenge. Herein, we show a gram-scale wet synthesis of Pt-1(1+) stabilized in a confined space by a crystallographically well-defined first water sphere, and with a second coordination sphere linked to a metal-organic framework (MOF) through electrostatic and H-bonding interactions. The role of the water cluster is not only isolating and stabilizing the Pt atoms, but also regulating the charge of the metal and the adsorption of reactants. This is shown for the low-temperature water-gas shift reaction (WGSR: CO + H2O CO2 + H…
Tracking Autoionizing-Wave-Packet Dynamics at the 1-fs Temporal Scale
2010
We present time-resolved studies and Fourier transform spectroscopy of inner-shell excited states undergoing Auger decay and doubly excited autoionizing states, utilizing coherent extreme-ultraviolet (XUV) radiation continua. Series of states spanning a range of ∼4 eV are excited simultaneously. An XUV probe pulse tracks the oscillatory and decaying evolution of the formed wave packet. The Fourier transform of the measured trace reproduces the spectrum of the series. The present work paves the way for ultrabroadband XUV spectroscopy and studies of ultrafast dynamics in all states of matter.
Plasmonic Focusing Reduces Ensemble Linewidth
2012
In this chapter I present an effect the coating of gold nanorods with a silver shell is evocating: a reduction of the ensemble plasmon linewidth by changing the plasmon-shape relation, which connects the particle shape with its plasmon resonance wavelength. This change, we term “plasmonic focusing” (Sect. 10.2), leads to less variation of resonance wavelengths for the same particle size distribution. Section 10.3 explains the effect of increasing single particle linewidth during the coating process, which is therefore not the reason for the observed ensemble linewidth decrease. This is rather a result from a change in the plasmon-shape relation explained in Sect. 10.4. Using a simple model,…
Interpretation of KPFM Data with the Weight Function for Charges
2018
The KPFM signal for systems containing local charges can be expressed as a weighted sum over all local charges. The weight function for charges quantifies the contribution of each charge, depending on its position. In this chapter, we evaluate the KPFM weight function for charges by analyzing several application-relevant model systems. The intention of this chapter is to provide insights into the KPFM contrast formation in order to facilitate the KPFM data interpretation. For this, we concentrate on three model systems: (A) a conductive sample in ultra-high vacuum, (B) a dielectric sample in ultra-high vacuum, and (C) a dielectric sample in water. We calculate the weight function for charge…
Kohn–Sham energy decomposition for molecules in a magnetic field
2018
We study the total molecular electronic energy and its Kohn–Sham components within the framework of magnetic-field density-functional theory (BDFT), an alternative to current-dependent density-functional theory (CDFT) for molecules in the presence of magnetic fields. For a selection of closed-shell dia- and paramagnetic molecules, we investigate the dependence of the total electronic energy and its Kohn–Sham components on the magnetic field. Results obtained from commonly used density-functional approximations are compared with those obtained from Lieb optimizations based on magnetic-field dependent relaxed coupled-cluster singles-and-doubles (CCSD) and second-order Moller–Plesset (MP2) den…
Linear-scaling self-consistent field theory based molecular dynamics: application to C60buckyballs colliding with graphite
2018
In this work, we investigate the collision of a C fullerene with graphite using large-scale molecular dynamics simulations, where the interatomic forces are computed ‘on-the-fly’ by means of self-c...
Compton scattering off nucleons near threshold
2008
The energy dependence of the magnetic polarizability β has been evaluated by use of the delta resonance in the s- and u-channel of the Compton scattering amplitude. It was the idea to extract the influence of higher order terms (higher than ω2, ω = |k| being the photon energy) in the analysis of the polarizability. The static paramagnetic polarizability βPara(0) has been substituted by an energy dependent βδPara(k) and the result is compared with experimental data.
Time-dependent density-functional theory of strong-field ionization of atoms by soft x rays
2014
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.