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[en] The superposition model is applied to the calculation of intrinsic parameters for each europium-ligand distance in LaCl3, LaAlO3, La2O3 and La2O2S. These parameters allow one to draw conclusions regarding the covalency of these compounds and, in some cases, to characterize the europium-ligand bonding. On the other hand, for weakly covalent compounds, the sigma* parameters may be determined by the angular overlap model
[fr]Le modele de superposition est applique au calcul des parametres intrinseques pour chacune des differentes distances des ligandes a l'ion dopant Eu3+, dans les composes LaCl3, LaAlO3, La2O3 et La2O2S. Ces parametres permettent de tirer des conclusions relatives a la covalence de ces matrices et de caracteriser, dans certains cas, la liaison europium-ligande. D'autre part, on determine, par le modele du recouvrement angulaire, des parametres sigma* dans le cas des composes faiblement covalents
[en] As a model for the electronic properties of Sm compounds and alloys showing configuration mixing we study the two-band Hubbard Hamiltonian generalized to include the interatomic Coulomb mechanism for configuration mixing suggested by Kaplan and Mahanti. This model can exhibit a localized mixed-configuration ground state as indicated by experiments on some alloys. The stability of this state against delocalization of the electrons is studied as a function of the parameters of the model
[en] Surface alloying is a powerful way of varying physical and chemical properties of metals, for a number of applications from catalysis to nuclear and green technologies. Surfaces offer many degrees of freedom, giving rise to new phases that do not have a bulk counterpart. However, the atomic characterization of distinct surface compounds is a major task, which demands powerful experimental and theoretical tools. Here we illustrate the process for the case of a GdAu2 surface phase of extraordinary crystallinity. The combined use of surface-sensitive techniques and state-of-the-art ab initio calculations disentangles its atomic and electronic properties. In particular, the stacking of the surface layers allows for gadolinium's natural ferromagnetic state, at variance with the bulk phase, where frustration leads to antiferromagnetic interlayer coupling.