Nanowire reconstruction under external magnetic fields.

We consider the different structures that a magnetic nanowire adsorbed on a surface may adopt under the influence of external magnetic or electric fields. First, we propose a theoretical framework based on an Ising-like extension of the 1D Frenkel-Kontorova model, which is analyzed in detail using the transfer matrix formalism, determining a rich phase diagram displaying structural reconstructions at finite fields and an antiferromagnetic-paramagnetic phase transition of second order. Our conclusions are validated using ab initio calculations with density functional theory, paving the way for the search of actual materials where this complex phenomenon can be observed in the laboratory.

Generalized nonlocal kinetic energy density functionals based on the von Weizsäcker functional.

We generalize the ideas behind the procedure for the construction of kinetic energy density functionals with a nonlocal term based on the structure of the von Weizsäcker functional, and present several types of nonlocal terms. In all cases, the functionals are constructed such that they reproduce the linear response function of the homogeneous electron gas. These functionals are designed by rewriting the von Weizsäcker functional with the help of a parameter β that determines the power of the electron density in the expression, a strategy we have previously used in the generalization of Thomas-Fermi nonlocal functionals.

An analysis of two local measures of the electronic localization: a comparison with the ELF and the exchange-correlation density results.

In this work we have explored the performance of two functions, recently proposed by Ayers [J. Chem. Sci.

The sigma delocalization in planar boron clusters.

The sigma delocalization plays an important role in the stability of small boron clusters; therefore, it is important to establish under which circumstances this delocalization contributes to the aromaticity of these molecules. In this work, using electron localization function (ELF) calculations, we show that sigma and pi electrons follow different patterns of delocalization. For sigma electrons the delocalization is mainly due to the p(sigma) radial overlapping which decreases with ring size, thus, considerable delocalization is expected for small rings, while for the pi subsystem, the Hückel rule of organic chemistry works successfully regardless of the cluster size.