We propose porous C-N-based structures for biocompatible magnetic materials that do not contain even a single metal ion. Using first-principles calculations based on density functional theory, we show that when patterned in the form of a kagome lattice, nonmagnetic g-C3N4 not only becomes ferromagnetic but also its magnetic properties can be further enhanced by applying external strain. Similarly, the magnetic moment per atom in ferromagnetic g-C4N3 is increased three fold when patterned into a kagome lattice. The Curie temperature of g-C3N4 kagome lattice is 100 K, while that of g-C4N3 kagome lattice is much higher, namely, 520 K. To date, all of the synthesized two- and three-dimensional magnetic kagome structures contain metal ions and are toxic. The objective of our work is to stimulate an experimental effort to develop nanopatterning techniques for the synthesis of g-C3N4- and g-C4N3-based kagome lattices.

Results of first-principles calculations on pure and doped aluminum clusters are analyzed using the electron localization function ͑ELF͒ to obtain a real-space representation of the electronic shell structure. Our results provide a quantitative analysis of the bonding nature and localization of charge in jelliumlike metal clusters and show that similar to atoms, ELF reproduces the electronic shell structure of clusters in real space.

International audienceMetallic melts above the liquidus temperature exhibit nearly Arrhenius-type temperature dependence of viscosity. On cooling below the equilibrium liquidus temperature metallic melts exhibit a non-Arrhenius temperature dependence of viscosity characterized by liquid fragility phenomenon which origin is still not well understood. Structural changes and vitrification of the Pd(42.5)Cu(30)Ni(7.5)P(20) liquid alloy on cooling from above the equilibrium liquidus temperature are studied by synchrotron radiation X-ray diffraction and compared with the results of first-principles calculations. Subsequent analysis of the atomic and electronic structure of the alloy in liquid and glassy states reveals formation of chemical short-range order in the temperature range corresponding to such a non-Arrhenius behavior. The first-principles calculations were applied to confirm the experimental findings

Using density functional theory with the generalized gradient approximation, we have studied the interaction between a single Pt atom and a carbon nanotube. The bridge adsorption site on the outer wall of nanotube is favorable. The curvature affects the binding strength. Compared to the larger nanotube, Pt could bind stronger to the outer wall of a small radius nanotube. For zigzag nanotube, the most stable site on the outer wall is the bridge site with the underlying CC bond being parallel to the axis of the nanotube, while for the armchair nanotube it is the bridge site with the underlying CC bond being tilted to the axis of the nanotube. The energy in average differs by ϳ1.5 eV for adsorbing on both sidewalls of small radius nanotube, while it decreases much for the larger nanotube. Either by penetrating the wall or by substituting one C atom on the wall, the Pt atom is found to be hard to diffuse from the outside to the inside. The studied charge density suggests the weak covalentlike bonding between Pt and C atoms.

We report a new method for the design of kagome lattices using zigzag-edged triangular graphene nanoflakes (TGFs) linked with B, C, N or O atoms. Using spin-polarized density functional theory we show that the electronic and magnetic properties of the designed kagome lattices can be modulated by changing their size and the linking atoms. The antiferromagnetic coupling between the two directly linked TGFs becomes ferromagnetic coupling when B, C or N is used as the linking atoms, but not for O atom linking. All the designed structures are semiconductors which can be synthesized from graphene atomic sheets by using electron etching and block copolymer lithography techniques. This study is a good example of how mathematical models can be used to construct magnetic nanostructures involving only s, p elements.

Design of stable Si-cage and Si-tube structures is of great importance to the fields of Si nanotechnology and microelectronics. In order to explore the possibility of constructing a Si nanotube by using the metal-stabilized and tube-shaped Si cluster W@Si12 as the basic unit, detailed first-principles calculations are performed to analyse the interactions of the dimers. It is found that the interactions are orientation dependent, and no interactions exist if stacking is along the sixfold axis. However, the W atom can be used as the spacer to link two units, resulting in a metastable structure. Due to the large surface stress in such a small one-dimensional system, sixfold stacking cannot be extended, and thus the trimer is not dynamically stable. Further, the most stable geometry for the dimer is seriously distorted. Consequently, it is difficult to construct a Si nanotube using this W@Si12 tube-shaped unit.

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