The presence of flat bands near Fermi level has been proposed as an explanation for high transition temperature superconductors. The bands of graphite are extremely sensitive to topological defects which modify the electronic structure. In this Rapid Communication, we found nondispersive flat bands no farther than 10 meV of the Fermi energy in slightly twisted bilayer graphene as a signature of a transition from a parabolic dispersion of bilayer graphene to the characteristic linear dispersion of graphene. This transition occurs for relative rotation angles of layers around 1.5\ifmmode^\circ\else\textdegree\fi{} and is related to a process of layer decoupling. We have performed ab initio calculations to develop a tight-binding model with an interaction Hamiltonian between layers that include the $\pi${} orbitals of all atoms and takes into account interactions up to third nearest neighbors within a layer.

The aim of this study was to prepare a novel targeting drug delivery system for 2-Methoxyestradiol (2ME) in order to improve the clinical application of this antitumor drug. It is based in nanoparticles (NPs) of titanium dioxide (TiO${}_2$) coated with polyethylene glycol (PEG) and loaded with 2ME. A complete IR and Raman characterization have been made to confirm the formation of TiO${}_2$–PEG–2ME composite. Vibrational modes have been assigned for TiO${}_2$, PEG, and 2ME and functionalized TiO${}_2$–PEG and TiO${}_2$–PEG–2ME. The observed variation in peak position of FTIR and Raman of each for these composites has been elucidated in terms of intermolecular interactions between PEG–2ME and TiO${}_2$, obtaining step-by-step the modification processes that were attributed to the conjugation of PEG and 2ME to TiO${}_2$ NPs. Modifying TiO${}_2$ NPs with PEG loaded with the 2ME drug revealed that the titanium dioxide nanocarrier possesses an effective adsorption capability, and we discuss their potential application as a system of drug delivery.

We describe a method for performing density-functional calculations for topologically disordered condensed matter. This method combines the recursion and the linear-muffin-tin-orbital (LMTO) methods, and uses the tight-binding representation. In the present version, the LMTO matrix elements are evaluated in the atomic-sphere approximation (ASA). Various levels of approximation for the ASA Hamiltonian, such as the two-center tight-binding one, are systematically derived and tested. The method is applied to crystalline bcc Fe and to amorphous ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$. Charge self-consistency is only treated for the average Fe and the average B atoms. The Fe-B bonding is found to be covalent. A Stoner theory is derived and used to describe the ferromagnetism. The structures of our density of states for ferromagnetic ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ agree in detail with reliable photoemission data.

We present a theory to describe the equilibrium states and nucleation phenomena in ferromagnetic tubular nanostructures. We show that, in a broad range of geometrical parameters, the magnetic state of a nanotube is a mixture of vortex states, at tube ends, and a uniform magnetization state along the tube axis. The incomplete vortex structures confined at the tube ends are growing domain walls which can be set in motion with external fields, current-driven techniques, or thermal assistance. We also show how the well-known nucleation problem can be better understood with basis in the theoretical model presented in this paper.

Based on the discovery of a simple scaling relation, a new technique for the investigation of the phase diagram of nanosized magnetic systems is proposed. By scaling the exchange interaction between magnetic moments, the magnetic phase diagram of currently lithographically produced particles can be obtained from those corresponding to much smaller systems. Such a technique reduces the computation time by several orders of magnitude, and provides a new approach to the investigation of the relative stability of distinct internal magnetic configurations of nanosized systems. The technique is illustrated by the determination of the phase diagram of cylindrically shaped Co particles.