Structure and stability of small zinc oxide clusters

The structure and stability of small neutral and positively charged zinc oxide (ZnO) _n clusters (n = 2−9) have been studied within the density functional theory. For n ≤ 7, the most stable clusters are shown to be flat rings; for n = 8, 9, the clusters are mainly three-dimensional cage structures. The energies and main channels of fragmentation of the clusters have been determined. It has been found that the fragmentation of the charged clusters with n > 6 occurs predominantly with formation of a (ZnO)₄⁺ ion, which explains the available mass spectrometric data on ionization of the zinc oxide clusters by electron impact.     

Structure and stability of clusters on metal surfaces

Small clusters of 3d metals Ni/Ni(001), Cu/Cu(001), 4d-Pd/Pd(001), Ag/Ag(001), 5d-Pt/Pt(001), and Au/Au(001) are investigated by semiempirical methods using multiparticle interatomic interaction potentials. It is shown that the same magic numbers (4, 6, and 9) are characteristic for all metals indicated; these numbers are determined by the symmetry characteristics of the clusters, related to the morphology of the fcc (001) substrate. It is shown for Pt/Pt(111) that small clusters of seven, ten, and more atoms are stable for the fcc (111) surface. This confirms that the magic numbers are associated with the symmetry of the clusters. Fiz. Tverd. Tela (St. Petersburg) 41, 1329–1334 (July 1999)     

Multiply charged clusters

We review progress made in understanding Coulomb explosion of multiply charged atomic clusters. Their collision with highly charged atomic ions leads to clusters in charge states as high as z=10 with little vibrational excess energy; these systems approach the Rayleigh limit. Phase transitions become evident at higher excess energies. Numerous studies have been devoted to C^z+₆₀, like collisions with surfaces, multi-coincidence fragmentation analysis and gas-phase reactions. Stability and decay of highly charged micrometer-sized droplets and of metal di- and trianions have been monitored in ion traps. Excitation by femtosecond laser pulses allows to unravel properties of highly charged transient cluster ions. To cite this article: O. Echt et al., C. R. Physique 3 (2002) 353–364.     

Coulomb instability of charged clusters

A model different from the Rayleigh model for Coulomb instability of charged metallic clusters is proposed. The two-component model of a metallic cluster in the quasi-classical approximation offers different critical charges depending on the type of charged particles. For small-sized parallelepiped clusters, the quantization of the electronic spectrum is taken into account. The critical sizes of Ag _N ^2? and Ag _N ^3? clusters are calculated in the framework of the proposed model. The results of calculations are in good agreement with experimental data. The Coulomb explosion of positively charged clusters Na _N ⁿ⁺ at 3≤n≤5 is explained qualitatively.     

Structure and stability of neutral and cationic AlnO clusters

In this paper various structural possibilities for AlnO neutral and cationic isomers were investigated by using the B3LYP/6-311G（3df） method. Calculations of this paper predicted the existence of a number of previously unknown isomers. The stabilities of the AlnO （n = 2 - 7） clusters with even n are greater than those with odd n, however the stabilities Of cationic ions have the opposite odd-even alternation. The mass spectra observations of Al17O^＋ and Al19O^＋ ions support our theoretical predictions on their stabilities.     

Stability of Positively charged metallic clusters

Recent experimental results on the stability of positively charged metallic clusters are analyzed. The stability of multiply positively charged spherical Pb_n-clusters can be explained by assuming that metallic-like screening begins to occur in clusters with approximately 30 or more atoms and becomes bulk-like in clusters with approximately 300 atoms or more. Linearly shaped clusters Pb_n ⁺⁺ are stable forn6, but cease to exist for energetic reasons ifn13 atoms. Results for the stability of two-fold positively charged transition-metal clusters are also given.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Fission of doubly charged iron and aluminium clusters

We present a statistical fragmentation study of doubly charged iron and aluminum clusters of less than 60 atoms. At low excitation energies we find that the evaporation of one charged monomer is the most probable decay channel (asymmetric fission). When the excitation energy increases there is a competition between evaporation of a charged monomer and a charged dimer. For higher energies the number of channels increases and the multifragmentation mode appears at about 2.5 eV/atom. Presented by M.E. Madjet at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

中性及带电钴团簇的密度泛函理论研究

本文采用基于自旋极化的密度泛函理论系统研究了 小尺寸钴团簇的几何结构和电子结构特性。随尺寸的递增,团簇的基态几何结构由一维演变为三维的几何构型。总磁矩随尺寸的增加线性递增,并呈现奇偶交替的现象。从所研究的系统中分离一个Co原子带正电的团簇体系需要的能量相对较大。本文对体系的电子亲和能（EA）以及离化势（IP）也进行了讨论。     

Fragmentation channels of neutral and charged sodium clusters

The Density Functional Formalism (with the local density approximation for exchange and correlation) is applied to jellium-like spherical particles to obtain heats of fragmentation of Na_n; Na⁺_n and Na²⁺_n (n ⩽ 90) following different decay paths. Masses of the fragments are analyzed resulting that the energetically more favorable channels are controlled by the tendency to fragments with a magic number of electrons, mainly 2 or 8. We have also obtained that, provided we consider parent clusters with the same number of electrons and decay modes involving a neutral fragment, the fragmentations of neutral and ionized clusters are very similar.     

Symmetric and asymmetric fission of charged sodium clusters

A deformed-jellium model is used to calculate the fission barrier height of Na ₂₄ ²⁺ → Na ₂₁ ⁺ +Na ₃ ⁺ and Na ₄₂ ²⁺ → 2Na ₂₁ ⁺ within the Kohn—Sham Density Functional Theory (i.e., including shell effects). Although the shape of the barrier obviously depends on the parametrization of the fission path, we have found that the barrier maximum corresponds to a configuration in which the emerging fragments are already formed and rather well apart. The two examples chosen serve to illustrate the influence of the electronic shell effects.     

Dissociation of doubly charged alkali metal clusters

We have studied the competition experimentally observed between fission and neutral atom evaporation, as dissociation channels of excited doubly charged sodium clusters, using the Density Functional Theory and the jellium model. The fission barrier has been obtained from an Extended Thomas-Fermi calculation including density gradient corrections to the kinetic energy of the electronic cloud. We discuss the influence of the coefficient of the density gradient term on the barrier height.