The lowest-energy geometric structures and isomers of freestanding ${\mathrm{Co}}_N$ clusters $(4\mathrm{}<~N<~60)$ and their corresponding magnetic moments are calculated using an evolutive algorithm based on a many-body Gupta potential and a self-consistent $\mathrm{spd}$ tight-binding method, respectively. We found an icosahedral growth pattern for the global minimum with some hcp and fcc structures for some particular sizes, whereas for the second isomer, distorted icosahedral structures are obtained in general. With the aim to study the possible coexistence of isomers within the experimental cluster beam we assumed an equilibrium distribution and calculated for each cluster size the different coexistent structures and the relative populations at room temperature. Our results show that the coexistence is present only at some particular sizes, in agreement with chemical-adsorption and photoionization experiments. Our self-consistent tight-binding calculations considering $3d,$ $4s,$ and $4p$ valence electrons for the magnetic properties show that the magnetic moments for the global minima and the second isomers are in general very similar except in a small region of $20<N<\mathrm{}40\mathrm{}$ atoms where the magnetic moment of the global minimum is smaller than that of the second isomer. We compare our results for the magnetic behavior of the global minimum with theoretical calculations available in the literature as well as with experimental results.

We present a theoretical study of the electronic and magnetic properties of iron systems in different environments: pure iron systems [dimer, bcc bulk, (100) surface, and free-standing iron monolayer], and low-dimensional iron systems deposited on Ag (100) surface (monoatomic linear wires, iron monolayer, planar, and three-dimensional clusters). Electronic and magnetic properties have been calculated using a recently developed total-energy first-principles method based on density-functional theory with numerical atomic orbitals as a basis set for the description of valence electrons and nonlocal pseudopotentials for the atomic core. The Kohn-Sham equations are solved self-consistently within the generalized gradient approximation for the exchange-correlation potential. Tests on the pseudopotential, the basis set, grid spacing, and k sampling are carefully performed. This technique, which has been proved to be very efficient for large nonmagnetic systems, is applied in this paper to calculate electronic and magnetic properties of different iron nanostructures. The results compare well with previous ab initio all-electron calculations and with experimental data. The method predicts the correct trends in the magnetic moments of Fe systems for a great variety of environments and requires a smaller computational effort than other ab initio methods.

We report a systematic study of the structural and magnetic properties of free-standing rhodium clusters $({\mathrm{Rh}}_N,$ $4<~N<~26).$ The geometrical structures of the global minima and lowest energy isomers were obtained with a semiempirical Gupta potential and employing a global evolutive search algorithm. The spin-polarized electronic structure and related magnetic properties of these geometries were calculated by solving self-consistently a $\mathrm{spd}$ tight-binding Hamiltonian. We determined the possible coexistence of different isomers and found that inclusion does not, in general, change significantly the magnetic moments obtained for the global minima structures. Results are compared with the experiment and with other theoretical calculations available in the literature.

The ground-state magnetic properties and related electronic properties of small ${\mathrm{Fe}}_{\mathit{N}}$ clusters are calculated by using an spd-band model Hamiltonian in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment per atom μ${\mathrm{¯}}_{\mathit{N}}$, the spin-polarized charge distribution within the cluster, and the sp and d electronic density of states. The calculated μ${\mathrm{¯}}_{\mathit{N}}$ (N≤15) are larger than the bulk value ${\mathrm{\mu }}_{\mathit{b}}$=2.21${\mathrm{\mu }}_{\mathit{B}}$. Small local sp magnetic moments are obtained, which in most cases are opposite to the dominant d magnetic moments (${\mathrm{\mu }}_{\mathit{s}\mathit{p}}$≃-0.1${\mathrm{\mu }}_{\mathit{B}}$, ${\mathrm{\mu }}_{\mathit{d}}$≃2.5–2.9${\mathrm{\mu }}_{\mathit{B}}$). The role of sp electrons and spd hybridization is discussed particularly, by comparison with previous d-band model calculations. The main quantitative effect obtained by including the sp electrons in the self-consistent calculations is a reduction of about 10% of the value of μ${\mathrm{¯}}_{\mathit{N}}$.

We have calculated the average magnetic moments per atom $\overline{\mu }$ of nickel clusters $\left({\mathrm{Ni}}_N\right)$ as a function of cluster size in the range $5<~N<~60$. The cluster geometries have been taken from molecular-dynamics simulations with a semiempirical many-body potential for $N<~20$, and for $N>\mathrm{}20\mathrm{}$ the same potential was used for a steepest-descent relaxation of icosahedral structures. The spin-polarized electronic structure has been calculated for those optimized geometries with a self-consistent tight-binding method considering the $3d$, $4s$, and $4p$ valence electrons. The results are discussed in comparison with recent experimental data and other theoretical calculations. The theory explains perfectly the magnetic moments up to $N\approx 16$ and the decreasing tendency of $\overline{\mu }$ with cluster size. With respect to the oscillations of the measured magnetic moment for larger $N$, the theory gives an explanation for the minima, which appear to be associated with an icosahedral growth pattern. The observed maxima are more difficult to reproduce and we discuss some plausible alternatives.