F. Reuse

Atomic arrangements in Ni7 and Ni8 clusters

Abstract First principles electronic structure studies of geometries, binding energies, and magnetic moment of Ni 7 and Ni 8 clusters have been carried out within a density functional scheme. Several geometries and the possible Jahn–Teller distortions were examined. The ground state of a Ni 7 cluster is found to be a capped octahedron while that of Ni 8 is a D 2 bisdisphenoid. In each case, the ground state has energetically close states with different geometries but same magnetic moment. Some of these geometries correspond to structures observed in N 2 adsorption experiments. Calculated magnetic moments and ionization potentials are compared with recent experiments.

N2 adsorption around small Nin (n=2−4) clusters

Abstract The nature of N 2 adsorption and its effect on the geometries, electronic structure and magnetism of Ni n ( n =2−6) clusters has been studied using a linear combination of atomic orbitals-molecular orbital approach within the local density functional scheme. The adsorption sites in small clusters are found to be similar to those on bulk surfaces. The principal effect of N 2 adsorption is a demagnetization upon saturation coverage. The NiNi bonds are dilated but the geometrical structures are left intact. The studies show that the recent chemical methods for determining the geometrical structure of clusters can provide information on structure of bare clusters.

Growth and Formation of Fullerene Clusters

Theoretical studies on the stability and electronic structure of small carbon clusters assuming chain, ring, bowl, and fullerene structures have been carried out using a linear combination of atomic orbitals molecular orbital approach within a density functional formalism. Our studies on clusters containing between 12 and 60 atoms indicate three regimes for the growth and formation of carbon clusters. In clusters containing less than 20 atoms, the most stable geometry is the ring arrangements. Between 20 and 28 atoms, clusters with very different geometry have comparable energies. For clusters with larger than 30 atoms, the fullerene structures are the most stable structures. An analysis of the electronic structure shows a distinct correlation between the geometry and the nature of electronic states.

Structural and dynamical properties of magnesium microclusters

We present systematic Density Functional Theory-Local Density Approximation computations for neutral Magnesium clusters Mgn withn≤13. For the smaller sizes the ground state structure is optimized starting from selected symmetries and allowing for relaxation, Jahn-Teller distorsion and spin polarization. For the larger sizes we perform a simulated annealing based on the ab-initio Molecular Dynamics. By the same method, we study the thermal and dynamical properties of Mg10 and Mg16. The general picture emerging from these computations shows that already atn ≈10 these clusters have acquired many characteristic features of metallic Magnesium.

Magnetoelectric effect in a hydrogen molecule

The symmetry breaking due to a magnetic field applied on a hydrogen molecule H2 generates an electric polarization. This magnetoelectric effect occurs for electrons in a triplet state provided the magnetic induction field is not aligned with the symmetry axis of the molecule.

Electronic structure and stability of charged beryllium clusters

Electronic structure studies on neutral, singly and doubly ionized Be n clusters (n ≤ 5) have been carried out in order to investigate the stability and observability of charged clusters. Our studies employ wave function expansion in terms of gaussian type orbitals and have been carried out within local spin density formalism. It is shown that although small doubly ionized clusters are unstable, they are protected from fragmentation by energy barriers. We illustrate this explicitly for trimers by presenting a Born-Oppenheimer surface of Be3, Be+ 3 and Be++ 3. It is argued that depending on their geometries, the observable doubly charged clusters can be generated through a one or two photons ionization. We also present results on the distribution of “hole charge” in doubly ionized clusters and show that a small cluster exhibits metallic like behaviour in regard to distribution of missing electronic charge.

Structural and Electronic Properties of Neutral and Charged Mgn Clusters (n ≤ 13 and n = 57, 69)

We present electronic calculations on neutral, cationic, anionic and doubly ionized Mgn clusters for n≤13 and n=57, 69. Our studies employ Gaussian basis functions, treat exchange-correlation effects via the local spin density approximation (LDA), and use pseudopotentials. We investigate the size evolution of the bonding for neutral and charged clusters, and show that already around n=10 there are clear signs of a jellium type behavior, suggesting that within LDA neutral and charged clusters from n=10 have acquired several of the characteristic features of the metallic state. The transition from metastability to stability for doubly charged cations is also studied.

Static electric dipole polarizability of small sodium aggregates

We present pseudopotential local-spin-density calculations of the static electric polarizability of sodium dimers and trimers and their respective cations. The electronic polarizabilities are obtained from self-consistent calculations in the presence of an external electric field, which is kept sufficiently small to avoid non-linear effects. The calculated polarizability tensor has a strong anisotropy directly related to the geometric and electronic structures of the molecules, the anisotropy being larger for the neutral clusters. The polarizabilities are averaged over the vibrational motion and rotations of the aggregates in order to be compared with the experimental measurements. The obtained values show an improvement in the agreement with experiment with respect to the values calculated in the spherical approximation.