We present a density-functional theoretical investigation of the electronic and magnetic properties of octametallic Cr-based molecular antiferromagnetic rings. The presence of the divalent magnetic ion M unbalances the charge and the spin of the parent Cr(8) ring, leading to a finite total spin in the molecules. Results are presented for Cr(8), i.e., [Cr(8)F(8)(O(2)CH)(16)] (1), and for Cr(7)M rings belonging to two different derivatives, i.e., [Me(2)NH(2)][Cr(7)MF(8)(O(2)CH)(16)], with M=Ni, Mn, Fe, and Cu, and Me=CH(3) (2, "green" derivative), and [Cr(7) NiF(3)(C(6)H(10)NO(5))(O(2)CH)(15) (H(2)O)] (3,"purple" derivative). Exchange interaction parameters have been extracted from broken-symmetry calculations and compared with the available experiments; in agreement with them, we find that exchange parameters are rather similar in the two derivatives, although somewhat larger in the "purple" derivative. The analysis of the electronic properties shows some differences depending on M, in particular in the size of the highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) gaps. For all the "green" rings we observe that the HOMOs are localized on the divalent ion site, while the HOMOs for the "purple" Cr(7)Ni have a more delocalized nature; LUMOs, instead, are, except for "green" Cr(7)Cu, localized on the Cr atoms opposite to the M site. We discuss how these findings may show up in terms of an asymmetric I-V curve in molecular junctions working in the sequential tunneling regime, or help in discerning the orientation of the molecules with respect to a surface, in scanning tunneling experiments.

We report an in-depth study on how spin information propagates at supramolecular scale through a family of heteroaromatic linkers. By density-functional theory calculations, we rationalize the behavior of a series of Cr(7)Ni dimers for which we are able to systematically change the aromatic linker thus tuning the strength of the magnetic interaction, as experimentally shown by low temperature micro-SQUID and specific heat measurements. We also predict a cos(2) dependence of the magnetic coupling on the twisting angle between the aromatic cycles in bicyclic linkers, a mechanism parallel to charge transport on similar systems

A plastic scintillating disc (NE102, 3cm thick, 1m diameter) has been designed for detecting charged pions in nuclear reactions at intermediate energy. A hole of 20cm diameter was made in the middle of the disc in order to allow for the beam passage through the detector. The originality of the detector consists of the simultaneous use of four very compact central Photo Multiplier Tubes (PMT) and eight peripheral PMTs in order to retrieve the hitting point of a charged particle onto the disc surface with a space resolution of ±3cm. The original method has been developed by using polar coordinates and only the Time-Of-Flight information (TOF) from three or four nearest PMTs, including at least one central PMT.

We present detailed first-principles calculations of the normal state electronic properties of the Bi2Sr2CaCu2O8 (Bi-2212) high TC superconductor by means of the linearized augmented plane wave (LAPW) method within the framework of density functional theory (DFT). We describe the crystal structure by the body-centered tetragonal (BCT) cell with space group I4/mmm and optimize its volume, c/a ratio and atomic positions by total energy and atomic-force minimization. The optimization of the cell leads to small but visible changes in the topology of the Fermi surface, rounding the shape of the CuO2 barrels, and moving both the BiO bands, responsible for the pockets near the M point, below the Fermi level. We have then studied the influence of the large distortions in the BiO plane observed in nature by means of an √2×√2 orthorhombic cell (with Bbmb space group). Differently to what has been observed in the literature for the Bi-2201 compound, we find that for Bi-2212 the orthorhombic distortion does not induce relevant changes to the binding energies of the BiO bands, conserving their metallic character.

An experimental investigation has been carried out on the properties of electromagnetic shower detectors, composed of a uniform array of plastic scintillating fibers and lead (50:35 by volume ratio) for photons in the energy range 600–1200 MeV. When the photon's incidence angle to the fiber axis is within ±2° an energy resolution of