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The neutral p-chloranil ͑2,3,5,6-tetrachloro-p-benzoquinone͒ and its radical anion have been extensively studied using the Car-Parrinello projector augmented wave method, which is an all-electron electronic structure method for first-principles molecular dynamics based on the local density approximation of density functional theory. Frequencies and eigenmodes are derived by fitting a system of harmonic oscillators to the moleculardynamics trajectories. The dependence of the bond lengths and vibrational frequencies on the molecular ionicity is discussed, and the electron affinity, Coulomb repulsion, and the spin-splitting parameter of p-chloranil are also derived. ͓S0163-1829͑96͒05318-0͔

Exchange bias effects have been induced along the perpendicular-to-film direction in nanostructures prepared by electron beam lithography, consisting of a ferromagnetic [Pt/Co] multilayer exchange coupled to an antiferromagnet (FeMn). As a general trend, the exchange bias field and the blocking temperature decrease, whereas the coercivity increases, as the size of the nanostructures is reduced.

The prototype compound for the neutral-ionic phase transition-namely, TTF-CA-is theoretically investigated by first-principles density functional theory calculations. The study is based on three neutron diffraction structures collected at 40, 90, and 300 K ͓M. Le Cointe et al., Phys. Rev. B 51, 3374 ͑1995͔͒. By means of a topological analysis of the total charge densities, we provide a very precise picture of intrachain and interchain interactions. Moreover, our calculations reveal that the thermal lattice contraction reduces the indirect band gap of this organic semiconductor in the neutral phase and nearly closes it in the vicinity of the transition temperature. A possible mechanism of the neutral-ionic phase transition is discussed. The charge transfer from TTF to CA is also derived by using three different techniques.