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We study single-electron transport in quench-condensed bismuth films. By lateral confinement, we select a specific cluster of about 10(3) atoms and use tunneling barriers that appear naturally during thin-film formation. A remarkable reversible increase of the sample conductance up to 5 times was found as the temperature was lowered from 11 to 4 K. We attribute this effect to a spontaneous distortion of the cluster shape and discuss its relation to a phase transition predicted for free metallic clusters.

A projected spherical basis is defined with the scope of treating deformed metallic clusters. It depends on a parameter that simulates the system deformation. When the deformation goes to zero the spherical-shell model states are obtained. The basis is tested, with positive results, in several applications for Na clusters. The present formalism predictions are compared with those obtained within other models. Such a basis is suitable for a realistic and a unified fashion description of spherical and deformed metallic clusters.

We study size-selected deposition of Ag/sub 19//sup +/ clusters on Pd(100) at total kinetic energies of 20 and 95 eV using thermal energy atom scattering and molecular-dynamics simulations. Contrary to the case of Ag/sub 7/ where fragmentation is crucial to explain the data, the deposition leads at low temperature to noncompact structures localized around the impact point. We propose a model in which morphology changes take place between 200 and 300 K resulting in well-separated compact structures.

It is predicted that the viscosity of clusters should enlarge the fission times of metallic clusters considerably compared to those calculated with a purely statistical model. This is analogous to the case of heavy-ion induced fission of hot nuclei, but the effect is predicted to be about a factor of 10 stronger in metallic clusters. Fission of ${\mathrm{Na}}_{18}^{2+}{\ensuremath{\rightarrow}\mathrm{Na}}_{9}^{+}{+\mathrm{N}\mathrm{a}}_{9}^{+}$ is discussed as an example.

A theoretical evaluation of inelastic transition amplitudes corresponding to collisions between low-energy electrons (up to 5 eV) and small metallic clusters is presented. The target is excited into a particle-hole state and the cross section is obtained in the Born approximation. The formalism is applied to the Na{sub 8} cluster. Form factors for the direct and exchange-correlation terms of the residual interaction are shown as well as angle-integrated cross sections as a function of the energy of the incident electron. These cross sections present resonances associated with quasibound states in the outgoing and/or incoming channels at incident energies related to the Na{sub 8} single-particle states through the {ital Q} values of the transitions. The results also show the importance of the inclusion of the residual exchange-correlation contribution. {copyright} {ital 1996 The American Physical Society.}

Energetics and dynamics of Coulombic fission of small doubly charged potassium clusters subsequent to the ionization of singly charged ones are investigated experimentally and theoretically. Fission is shown to occur predominantly via ${\mathrm{K}}_{\mathit{n}}^{++}$\ensuremath{\rightarrow}${\mathrm{K}}_{\mathit{n}\mathrm{\ensuremath{-}}3}^{+}$+${\mathrm{K}}_{3}^{+}$ for 5\ensuremath{\le}n\ensuremath{\le}12. The close correspondence between the measured and the calculated kinetic energy release accompanying the fission process allows a deeper understanding of the dynamics and energy redistribution mechanisms in fission of metallic clusters.

The coupling to two particle-two hole configurations is at the basis of the calculations of the spreading width of the collective excitations that in random phase approximation (RPA) are described as superpositions of one particle-one hole elementary modes. Second RPA (SRPA) is just the extension of RPA including both kinds of configurations. In SRPA use is made of the quasiboson approximation (QBA) as in RPA. It has been found that this is at the origin of the fact that the coupling among them strongly lowers the RPA collective excitations, both in metallic clusters and in nuclei. When the coupling of the two particle-two hole configurations among themselves is also included, as it has to be done in order to be consistent, this effect is even enhanced. Thus the reasonably good description of the collective vibrational states obtained at the RPA level (as expected on physical grounds, for example, for the dipole modes) is completely spoiled in SRPA. In the present paper we show quantitatively, for metallic clusters, that this disturbing behavior is eliminated when no use is made of QBA and a better description of ground-state correlations is introduced.

We present a fully ab initio ultrafast spin manipulation calculation in two-magnetic-center clusters with CO attached to one of the magnetic centers. CO serves as an experimental marker for certain magnetic states between which spin flip and transfer can be achieved. The predicted spin-state-dependent CO vibrational frequencies indicate that spin manipulation can be readily monitored through the infrared spectrum. The feasibility is demonstrated by two charged clusters ${[{\text{CoMg}}_{2}\text{Ni-CO}]}^{+}$ and ${[\text{NiCo-CO}]}^{+}$. Spin transfer between magnetic centers is achieved with a fidelity of 99.8%.

We show by molecular dynamics simulations that the melting temperature of clusters can be tuned by selective doping. In fact, a single Ni or Cu impurity in Ag icosahedral clusters considerably increases the melting temperature even for sizes of more than a hundred atoms. The upward shift is correlated to the strain relaxation induced by a small central impurity in icosahedral clusters.

The Moebius inversion pair potential has been employed, in combination with genetic algorithms, to predict the lowest-energy structures of the rare-earth metallic clusters La{sub N}, Ce{sub N}, and Pr{sub N} (N=3--20). Results are given for the symmetries, binding energies, nearest-neighbor distances of these clusters, and lowest-energy configurations of Ce{sub N} clusters. Also, the calculated second finite difference of the total energy shows that for three species elements, the 13-atom clusters with I{sub d} symmetry are particularly stable. Some minor peaks are also found at size N=4, 6, 11, and 15, which indicates that the corresponding clusters are relatively stable in structure. Present work points out a route to studying clusters.