Ab initio study of MF2 (M=Mn, Fe, Co, Ni) rutile-type compounds using the periodic unrestricted Hartree-Fock approach

The ab initio periodic unrestricted Hartree-Fock method has been applied in the investigation of the ground-state structural, electronic, and magnetic properties of the rutile-type compounds MF2 (M=Mn, Fe, Co, and Ni). All electron Gaussian basis sets have been used. The systems turn out to be large band-gap antiferromagnetic insulators; the optimized geometrical parameters are in good agreement with experiment. The calculated most stable electronic state shows an antiferromagnetic order in agreement with that resulting from neutron scattering experiments. The magnetic coupling constants between nearest-neighbor magnetic ions along the [001], [111], and [100] (or [010]) directions have been calculated using several supercells. The resulting ab initio magnetic coupling constants are reasonably satisfactory when compared with available experimental data. The importance of the Jahn-Teller effect in FeF2 and CoF2 is also discussed.

El món deis adolescents: propostes per a observar i comprendre

Al llarg de dos cursos (2002-2004) un grup de professionals implicats en la intervenció educativa i en la investigació va dur a terme la investigació-acció "El món" dels adolescents explicat per ells rnaleixos". Les pagines que segueixen són un petit resum d'alguns dels seus capítols, fonamentalment d' aquells que plantegen una altra manera de mirar-se i d'e ntendre I'adolescencia. L'estatus contradictori de I'adolescencia i les seves consideracions sobre la fe licitat condueixen al debat sobre la responsabililat. No té cap mena de sentit considerar I'adolescencia com un estadi d' irresponsabilitat general.