Narrow Results

This paper gives a survey of physical phenomena manifesting themselves in electron and photon collisions with atomic clusters. The emphasis is made on electron scattering, photoabsorption and photoionization of fullerenes and metal clusters, however some results are applicable to other types of clusters as well. It is demonstrated that the diffraction and interference phenomena play an important role in the processes of clusters interaction with photons and electrons. The essential role of the multipole surface and volume plasmon excitations is elucidated in the formation of electron energy loss spectra on clusters as well as in the total inelastic scattering cross sections and in multiphoton absorption regime. Attention is paid to the elucidation of the role of the polarization interaction in low energy electron-cluster collisions. This problem is considered for the electron attachment to metallic clusters and the plasmon enhanced photon emission. The mechanisms of electron excitation widths formation and the relaxation of electron excitations in metal clusters and fullerenes are discussed.

This work is devoted to the elucidation of the applicability of the jellium model to the description of alkali cluster properties. We compare the jellium model results with those derived within ab initio theoretical approaches and with experiments. On the basis of Hartree–Fock and local-density approximations we have calculated the binding energies per atom, ionization potentials, deformation parameters and optimized values of the Wigner–Seitz radii for neutral and singly charged sodium clusters with the number of atoms N ≤ 20. The characteristics calculated within the framework of the deformed jellium model are compared with the results derived from ab initio simulations of cluster electronic and ionic structure based on density functional theory and systematic post Hartree–Fock many-body perturbation theory accounting for all electrons in the system. The comparison performed demonstrates the great role of the cluster shape deformations in the formation cluster properties and quite reasonable level of applicability of the deformed jellium model. This elucidates the similarities of atomic cluster physics with the physics of atomic nuclei.

Advances achieved during recent years in model and ab initio descriptions of fission of metal clusters are reviewed. We focus on developments in ab initio treatment of the electronic subsystem within the jellium background model, as well as on applications of potential energy surface analysis to determining the characteristics of the fission process. We reiterate the main results obtained with the implementation of the Hartree–Fock and local density schemes for the two-center deformed jellium model. We overview the influences of the geometrical and statistical factors on the parameters of the fission process revealed recently. Also, we overview concisely the classical liquid drop model, the shell correction method, the asymmetric two-center-oscillator shell model, and the main approaches to the molecular dynamics simulations of the fission process.

CO chemisorption on PVP-protected Pt clusters supported on fine high silica zeolite Beta has been studied by in situ FTIR spectroscopy. Two special CO adsorption bands are observed at 2050 cm^-1 and 1860 cm^-1, respectively, on the surface of catalysts. The frequency shifts and CO band intensity vary with the changing of catalyst preparation parameters, such as polymer amount, Pt loading and pretreatment processing. The results show that PVP-protected Pt clusters have high dispersion on Beta zeolite surface and strong chemical adsorption to CO.

Effect of ligand exchange on the optical and photoluminescence properties of Au₂₅SG₁₈ (SG-glutathione thiolate) clusters was investigated. A fluorescein-based dye, 5-((2-(and-3)-S-(acetylmercapto)succinoyl)amino)-fluorescein (SAMSA) was anchored on water soluble Au₂₅SG₁₈ clusters by the place exchange reaction and the solid-state emission of the exchange product was studied. Inherent fluorescence image of these clusters was mapped. Organic soluble Au₂₅(SC₂H₄Ph₁₈ clusters were synthesized as a model system which also showed temperature-dependent solid-state emission, in good agreement with the results from water soluble Au₂₅ clusters.

In this paper we focus on the use of electron density and current-density as basic variables in describing a many-electron system. We start with a discussion of the seminal Thomas–Fermi theory and its extension by Bloch for time-dependent hamiltonians. We then present modern density-functional theory (for both time-independent and time-dependent hamiltonians) and approximations involved in implementing it. Also discussed is perturbation theory in terms of electron density and its use for calculating various response properties and related quantities. In particular, van der Waals coefficient C₆ is calculated using density and current density in time-dependent perturbation theory. Throughout the paper, results for alkali-metal clusters are presented to demonstrate the strength of density-based theories.

A comprehensive theoretical study on the structure and stability of linear and triangular isomers of anionic clusters of zinc, cadmium and mercury and their binding with one and two alkali metal cations (X⁺ = Li⁺, Na⁺, K⁺) has been investigated at the density functional (BP86 and B₃LYP) and ab initio (MP₂, MP₄ and coupled cluster single and double (CCSD)) methods. The results showed that in all cases, the triangular geometry with D_3h symmetry is more stable than linear one. The calculated values of interaction energies (IE) between anions and two X⁺ cations, Wiberg bond indices (WBI) and the electron densities at bond critical points (BCP), ρ(BCP), for Y–X bonds show that among all complexes investigated here at all levels of theory Zn₃Li₂ and Hg₃K₂ have the largest and the smallest values of IE, WBI and ρ(BCP), respectively. The natural charges of the atoms and WBI involved in the bonding as well as the global value of the charge transfer ΔQ from to X⁺ cation in X₂Y₃ clusters, evaluated through natural population analysis, confirmed that covalent contribution in Y–X bond formation increases from K⁺ to Li⁺. Also the energy decomposition analyses (EDA) were used to detect the nature of interaction in the complexes. The results confirmed that the contribution of electrostatic interactions in present complexes is almost more than 70%.

We present a recently introduced hierarchical model for the description of clusters in contact with an environment (embedded or deposited cluster). We briefly outline the ingredients of the model and show the relevance of a proper treatment of the degrees of freedom of the environment. We then discuss the effects of cluster–substrate interaction in three different dynamical scenarios: optical response of a small Na cluster deposited on an MgO surface, a comparison of the dynamics of deposition of an Na cluster on an MgO surface versus an Ar surface, and strong laser excitation of an Na cluster embedded in an Ar matrix.

We present a recently introduced hierarchical model for the description of clusters in contact with an environment (embedded or deposited cluster). We briefly outline the ingredients of the model and show the relevance of a proper treatment of the degrees of freedom of the environment, taking as example the optical response of a small embedded metal cluster. We finally discuss the technical and formal difficulties raised by a proper treatment of the Self Interaction Correction problem in a true dynamical situation.