M. Pereiro

Unexpected Magnetism of Small Silver Clusters

The ground-state electronic and magnetic properties of small silver clusters Ag{sub n} (2{<=}n{<=}22) have been studied using a linear combination of atomic Gaussian-type orbitals within the density functional theory. The results show that the silver atoms, which are diamagnetic in a bulk environment, can be magnetic when they are grouped together in clusters. The Ag{sub 13} cluster with icosahedral symmetry has the highest magnetic moment per atom among the silver clusters studied. The cluster symmetry and the reduced coordination number specific to small clusters are revealed as a fundamental factor for the onset of magnetism.

Structure of small silver clusters and static response to an external electric field

The static response properties and the structural stability of silver clusters in the size range

Model potential nonlocal density functional calculations of small cobalt clusters, Con,n⩽5

1\le n \le 23

Block copolymer-regulated synthesis of gold nanocrystals with sharp tips and edges

have been studied using a linear combination of atomic Gaussian-type orbitals within the density functional theory in the finite field approach. The Kohn-Sham equations have been solved in conjuction with a generalized gradient approximation (GGA) exchange-correlation functional. A proof that the finite basis set GGA calculation holds the Hellmann-Feynman theorem is also included in the Appendix. The calculated polarizabilities of silver clusters are compared with the experimental measurements and the jellium model in the spillout approximation. Despite the fact that the calculated polarizabilities are in good agreement with both of them, we have found that the polarizability appears to be strongly correlated to the cluster shape and the highest occupied-lowest unoccupied molecular-orbital gap.

Biomedical applications of small silver clusters

Abstract The results of self-consistent nonlocal generalized gradient approximation (GGA) density functional calculations are reported for small cobalt clusters Co n (2⩽n⩽5) . An emphasis is made on a proper treatment of exchange and correlation effects. The enhancement of the magnetic moments as well as the bonding properties of these clusters are discussed in terms of the cluster size and symmetry. We compare some results from deMon–KS (D) module release 3.2 and the computational scheme of Sambe–Felton and Dunlap (SFD).

Fusarium moniliforme keratitis

Gold decahedra and triangular plates of small size (30 and 50 nm, respectively) were grown by a green one-step synthesis process of HAuCl4 in the presence of citric acid and amphiphilic copolymer Tetronic T904® (from BASF), which both act as reducing and stabilizing agents. Tetronic T904® is a star-shaped copolymer composed of polyethylene oxide and propylene oxide units. Both compounds are key in the formation of decahedral particles due to their specific adsorption on certain crystallographic planes of the nanoparticles. Withdrawal or substitution of one of them involves the formation of irregular particles. On the other hand, by changing the reactions conditions the nanoparticle size and shape could be modified. In particular, by varying the molar ratio between the block copolymer a more efficient protection provided by the block copolymer is achieved, which allows the reaction to turn into kinetic control and, thus, a change from decahedral to triangular shape is observed. Due to the presence of acute tips and sharp edges, which sustain large electromagnetic fields upon excitation with light of appropriate energy, these nanoparticles demonstrated their utility as SERS substrates. Concentrations of up to ∼10−11 M of the Raman probe 4-nitrobenzenethiol displayed a readable SERS spectrum, with electromagnetic enhancement factors of up to ∼4.2 × 107.

Magnetic-dependent structure in eight-atom gold clusters

The ground-state properties of small silver clusters Agn (2⩽n⩽24) have been studied using a linear combination of atomic Gaussian-type orbitals within the density functional theory. The results show that the Ag13 clusters, due to their noticeable magnetic moment and their considerable highest occupied-lowest unoccupied molecular orbital gap, are promising candidates for the magnetic applications of nanoparticles. In particular, our study suggests that the silver nanoclusters made out of Ag13 clusters, as building blocks, are suitable for possible future applications in biomedicine, since they could improve some present-day difficulties of magnetic nanoparticles such as toxicity and opsonization.

Las micosis por Trichophyton megninii en Galicia (Con revisión de la taxonomia de este dermatofito)

Abstract We report a case of keratomycosis from which fusarium moniliforme was isolated. After initial therapy without improvement, antifungal testing showed susceptibility to cyclopiroxolamine. After changing to this treatment the infection improved and an eventual healing took place with moderate corneal scarring.

Calculations of giant magnetoresistance in Fe/Cr trilayers using layer potentials determined from ab initio methods

We have performed ab initio calculations on the lowest energy structure of eight-atom gold clusters, a tetracapped square with D4h symmetry, locking it to several total magnetic moments. We have found that for nonzero values of the total magnetic moment, the D4h symmetry is not stable. We have also found that for a fixed nonzero total magnetic moment, the stable structure is a distortion of the tetracapped square, along the square’s diagonals. This structure has a D2h symmetry. The rest of possible structures for this cluster have been calculated as well, and no magnetism-dependent deformation was found, except for the tetracapped tetrahedron with symmetry Td, which is unstable for nonzero total magnetic moment. In this case, the favored structure is a bicapped octahedron with symmetry D2d. The structural change due to magnetic constraints is relevant since the surface of gold clusters has shown a catalytic behavior highly dependent on the structure.

Electronic structure analysis of the quasi-one-dimensional oxide Sr6Co5O15 within the LDA+U method

The taxonomy of the dermatophyte Trichophyton megninii has been the subject of much discussion since it was first isolated by Sabouraud in 1893. Initially he named it Trichophyton a culture rose and later T. rosaceum. It has been confused with the Microsporum (Epidermophyton) gallinae described by Megnin.Nowadays most mycologists consider T. rosaceum to be a synonym of the T. megninii, although some French authors still use Sabourauds denomination.It is an exclusively anthropophilic dermatophyte with a broad geographic distribution, but in general a low incidence in most countries, except in Portugal, Corsica and Sardinia where it causes infections of both hairy and glabrous skin zones and nails in humans.T. megninii is an uncommon cause of ringworm in Spain and is mainly restricted to Galicia, and even there the incidence is low; it has been isolated only five times in our clinical practice with two more cases described previously in the literature, and predominantly affects females. Case reports show t...