## Search

Now showing items 1-10 of 99

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Aufsatz
Slave-boson approach to the size-dependent transition from van der Waals to covalent bonding in Hg_n clusters

(1994)

We use a microscopic theory to describe the dynamics of the valence electrons in divalent-metal clusters. The
theory is based on a many-body model Harniltonian H which takes into account, on the same electronic level, the
van der Waals and the covalent bonding. In order to study the ground-state properties of H we have developed an
extended slave-boson method. We have studied the bonding character and the degree of electronic delocalization in
Hg_n clusters as a function of cluster size. Results show that, for ...

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Aufsatz
Unrestricted hartree-fock calculation of the ionization potential of small Hg_n clusters

(1993)

The ionization potential of small Hg_n clusters has been calculated. For the first time
good agreement with experimental results has been obtained. It is shown that interatomic
Coulomb interactions are important. The energy of Hg_n^+ is calculated using the unrestricted inhomogeneous Hartree-Fock approximation. As a consequence of a change in the charge distribution in Hg_n^+ , we obtain an abrupt change in the slope of the ionization potential at the critical cluster size n_cr ~ 14. The presented results are ...

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Aufsatz
Theory for the optical properties of small Hg_n clusters

(1991)

The static and dynamical polarizabilities of the Hg-dimer are calculated by using a Hubbard Hamiltonian to describe the electronic structure. The Hamiltonian is
diagonalized exactly within a subspace of second-quantized electronic states from which only multiply ionized atomic configurations have been excluded. With this approximation
we can describe the most important electronic
transitions including the effect of charge fluctuations. We analyze the polarizability as a function of the intraatomic Coulomb interaction ...

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Aufsatz
Delocalization of a hole in van der Waals clusters: Ionization potential of rare-gas and small Hg_n clusters

(American Physical Society, 1993)

The size dependence of the ionization potential I_p(n) of van der Waals (vdW) bound clusters has been calculated by using a model Hamiltonian, which includes electron hopping, vdW interactions, and charge-dipole interactions. The charge-density and dipole-density distributions for both neutral and ionized n-atom clusters are determined self-consistently. The competition between the polarization energy of the neutral atoms surrounding a partially localized hole and the tendency toward hole delocalization in the ionized ...

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Aufsatz
Theory for Optical Absorption in Small Clusters: Dependence on Atomic Structure and Cluster Size

(American Physical Society, 1994)

We present a theory which permits for the first time a detailed analysis of the dependence of the absorption spectrum on atomic structure and cluster size. Thus, we determine the development of the collective excitations in small clusters and show that their broadening depends sensitively on the tomic structure, in particular at the surface. Results for Hg_n^+ clusters show that the plasmon energy is close to its jellium value in the case of spherical-like structures, but is in general between w_p/ \wurzel{3} and ...

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Aufsatz
On the transition from localized to delocalized electronic states in divalent-metal clusters

(1991)

The transition from van der Waals to covalent
bonding, which is expected to occur in divalent-metal clusters with increasing cluster size, is discussed. We propose
a model which takes into account, within the same electronic theory, the three main competing contributions, namely the kinetic energy of the electrons, the Coulomb
interactions between electrons, and the s \gdw p intraatomic transitions responsible for van der Waals like bonding.
The model is solved by taking into account electron correlations
using ...