A. Vega

Study of the Structural and Electronic Properties of RhN and RuN Clusters (N < 20) within the Density Functional Theory

Using the density-functional theory (DFT) with the generalized gradient approximation to exchange and correlation, we compute the geometries, electronic structure, and related properties of free-standing rhodium and ruthenium atomic clusters with sizes below 20 atoms. We explore different structural and spin isomers per size, for which we determine the interatomic distances, binding energy, magnetic moment, HOMO-LUMO gap, and electric dipole moment. For many sizes, different implementations of DFT predict different properties for the lowest-energy isomers, thus illustrating the complex nature of these 4d transition metal elements at the nanoscale. We discuss our results for rhodium clusters in the context of recent electric deflection measurements.

Structural and magnetic properties of X12Y (X, Y=Fe, Co, Ni, Ru, Rh, Pd, and Pt) nanoalloys

We perform extensive ab initio density-functional calculations to investigate the structures and magnetic moments of the binary clusters X12Y (X, Y=Fe, Co, Ni, Ru, Rh, Pd, and Pt). Although all the binary clusters Fe12Y, Co12Y, Ru12Y, and Rh12Y, plus Ni12Y (Y=Rh, Pd, and Pt) and Pt12Y (Y=Ru, Rh, and Pd), retain, with more or less distortions, the structures of the corresponding pure X13 clusters, the remaining binary clusters (i.e., a significant number of 12 of all the 42 cases) adopt geometries different from those of the corresponding pure clusters. Independent of the peculiarities of each family of binary clusters, the binding energies of all the binary clusters X12Ru are bigger than those of the pure X13 clusters, while the binding energies of all the binary clusters X12Pd are smaller. The clusters investigated exhibit a variety of magnetic behaviors. In the case of Ni12Rh, we predict a remarkable magnetic cooperative phenomenon that can be attributed to electronic effects associated to the chemical ...

All-electron and pseudopotential study of the spin-polarization of the V(001) surface: LDA versus GGA

The spin-polarization at the V(001) surface has been studied by using different local [local spin-density approximation (LSDA)] and semilocal [generalized gradient approximation (GGA]) approximations to the exchange-correlation potential of DFT within two ab initio methods: the all-electron tight-binding linear muffin-tin orbital atomic-sphere approximation and the pseudopotential linear combination of atomic orbitals code SIESTA (Spanish initiative for electronic simulations with thousands of atoms). A comparative analysis is performed first for the bulk and then for a N-layer V(001) film

Ab initio study of the adsorption of NO on the Rh6(+) cluster.

(7l~Nl~15).

Stability, structural, and magnetic phase diagrams of ternary ferromagnetic 3d-transition-metal clusters with five and six atoms.

The LSDA approximation leads to a nonmagnetic V(001) surface with both theoretical models in agreement (disagreement) with magneto-optical Kerr (electron-capture spectroscopy) experiments. The GGA within the pseudopotential method needs thicker slabs than the LSDA to yield zero moment at the central layer, giving a high surface magnetization (1.70 Bohr magnetons), in contrast with the nonmagnetic solution obtained by means of the all-electron code.

C(2 × 2) ferrimagnetic order versus P(1 × 1) ferromagnetic order in V, Cr, Mn monolayers on Fe(001)

The process of NO adsorption on the cationic cluster Rh(6)(+) is investigated using the density-functional theory (DFT) with the generalized gradient approximation (GGA) to exchange and correlation. We determine the geometries, electronic structure, and relevant energies for different structural and spin isomers of Rh(6)(0,±), and we study the consecutive adsorption of two NO molecules on the cationic cluster Rh(6)(+). With regard to the first NO molecule, different adsorption energies are found for the ground state octahedral structure of the bare cationic cluster and for the first isomer, which, having a prism-type structure, undergoes a structural transition to an octahedral symmetry upon dissociative adsorption of NO. Several dissociative NO adsorption processes are analyzed in comparison with molecular adsorption of NO to give support to the first step of the reaction inferred from experiments. With regard to the adsorption of a second NO molecule, the intermediate with lowest energy contains a preformed N(2) molecule. The energy of that complex is about 0.7 eV smaller than the sum of the free N(2) energy plus the lowest energy of the Rh(6)(+)-O(2) complex. This complex is composed of two separated O atoms occupying adjacent 2-fold bridging positions of the nearly undistorted Rh(6)(+) octahedral cluster. These findings are in qualitative agreement with experiments.

Insulating or Metallic: Coexistence of Different Electronic Phases in Zinc Clusters

We report a theoretical investigation of free-standing Fe(x)Co(y)Ni(z) ternary clusters with x + y + z = 5 and 6. Our study is performed within density functional theory as implemented in the GAUSSIAN 03 set of programs and with the BPW91/SDD level of theory. We analyze the geometries, chemical order, local and total magnetic moments, binding energies, excess energies, and second difference in the energy in the whole range of composition, from which structural, magnetic, and stability phase diagrams are predicted for these cluster sizes. We determine the optimal stoichiometries for these clusters as regards the maximum total magnetic moment and stability.

A density-functional study of the possibility of noncollinear magnetism in small Mn clusters using SIESTA and the generalized gradient approximation to exchange and correlation.

Abstract The possibility of a ferrimagnetic-in-plane configuration with C(2 × 2) symmetry is analyzed for V, Cr and Mn monolayers deposited on Fe(001). The spin-polarized electronic distribution is calculated by solving self-consistently a tight-binding Hamiltonian in a mean field approximation. The relative stability of this solution with respect to the usual P(1 × 1) ferromagnetic-in-plane solution is determined by means of the difference of total energy. A nearly zero surface magnetization is obtained in the C(2 × 2) arrangement. The results of this study are discussed in relation with recent experimental observations.

Impact of dimerization and stretching on the transport properties of molybdenum atomic wires

How many of the several attributes of the bulk metallic state persist in a nanoparticle containing a finite number of atoms of a metallic element? Do all those attributes emerge suddenly at a well-defined cluster size or do they rather evolve at different rates and in a broad size range? These fundamental questions have been addressed through a conjoint experimental/theoretical investigation of zinc clusters. We report the observation of novel coexistence phenomena involving different electronic phases: for some sizes, metallic and insulating electronic states coexist within a single, Janus-like, nanoparticle; for the rest of sizes, we report the coexistence of two weakly interacting metallic phases with different dimensionalities, localized at the shell and the core of the nanoparticle. These fascinating features are due to an anomalously long core-shell separation that equips the shell and core regions with largely independent structural, vibrational, and thermal properties.

Metallic behavior of Pd atomic clusters

We investigated the possibility of noncollinear magnetism in small Mn(n) clusters (n=2-6) using the density-functional method SIESTA with the generalized gradient approximation (GGA) to exchange and correlation. The lowest-energy states identified were collinear, with the atomic spin magnetic moments pointing in the same direction, for Mn(2) and Mn(3), and noncollinear for Mn(4), Mn(5) and, most decidedly, Mn(6). These SIESTA/GGA results, which are compared with those of an earlier SIESTA study that used the local spin density approximation, are qualitatively in keeping with the result obtained by VASP/GGA calculations.