J.M. Cabrera-Trujillo

A possible route to macroscopic formation of endohedral fullerenes

Abstract A possible mechanism to encapsulate atoms in the internal cavities of C 60 and higher fullerenes is proposed. It involves the production of C 60 molecules with two carbon isotopes A C and B C ( A , B = 12, 13, 14). The molecules A C 59 B C 1 and A C 58 B C 2 are separated from the total production and collected in a chamber under partial pressure of the element to be inserted. The proposed mechanism is to excite selectively the minority isotopes by laser irradiation in such a way that the bonds formed by the excited atoms are stretched to open a gate, allowing the foreign atoms to get into the distorted cages. The calculation of the electronic structure and the energy needed to deform C 60 supports this insertion mechanism.

Local electronic density of states in two-component penrose lattices

Abstract The electronic structure of two-component Penrose models of quasicrystals is studied by using a tight-binding model. The Penrose lattice is subdivided in non-equivalent sublattices and the local density of states are calculated at a site surrounded by clusters of distinct sizes. The strong dependence of the density of states on the cluster size and the local neighborhood is evidenced. In particular, the electronic structure of a decoration proposed to model the T-phase of AlFe, is calculated. An asymmetric density of states with no self-similar behaviour is obtained.

Size Effect and Shape Stability of Nanoparticles

Nanoparticle research disciplines—chemical synthesis, applied physics and devices based on their physical-chemical properties, and computational physics—have been very active fields for the last 15 years or so, because of the potential and current applications in medicine, catalysis, energy storage, environment and electronics applications. This wide spectrum of disciplines and their applications keep metallic nanoparticles as one of the most promising nanostructures and their research as one of the cornerstones of nanotechnology. In this contribution we present a comprehensive and extended geometrical description for the most common shapes and structures for metallic nanoparticles, as well as experimental results for these geometries with some variations given by truncations.

Molecular dynamics approach for crystal structures of methane A and B

The carbon structures of phases A and B of methane are investigated through classical molecular dynamics simulations using optimized potentials for liquid simulations all-atom force fields as well as ReaxFF reactive force fields. Both final thermodynamic states were obtained by the proper ramping of temperature and pressure through well-known regions of methane’s phase diagram using the isothermal–isobaric (NPT) ensemble. Our calculated structures are in good agreement with very recent experimental data. The knowledge of these phases is the basis for the study of methane at high pressures.

ATOMIC AND ELECTRONIC STRUCTURE OF QUASICRYSTALS

Some models used to describe the experimental diffraction pattern observed in icosahedral quasicrystals, are presented. Particular atention is given to the interpretation of diffraction patterns in terms of regular crystals of higher dimensions. Two special cases, the Fibonacci chain and the two dimensional Penrose lattice are discussed in detail. The electronic structure of these models are analyzed within the tight–binding Hamiltonian. Results for the local density of states and the behavior of the wave functions, in Fibonacci chains, using renormalization techniques are discussed. In the case of two dimensional systems, the local density of states of Penrose clusters of various sizes, generated by deflation rules, are calculated. Two techniques, the continued fraction method and the cluster Bethe lattice method, are used to solve the equations of motion of the Green function. To model the AIMn and AIFe systems, the Penrose lattice is subdivided into non–equivalent sublattices and the Voronoi cells are decorated. The main characteristics of the electronic spectra of particular biatomoc arrangements are discussed.