Structural properties of the (NaCl-type) and (CsCl-type) phases of alkaline-earth oxides and their phase transition have been investigated with the periodic ab initio linear combination of atomic orbitals method implemented in the CRYSTAL program. The geometries have been optimized and the bulk modulus evaluated. The calculations have been done at the Hartree-Fock (HF) and density functional theory (DFT) levels. In this last case, the exchange-correlation potential correcting the electronic density uses either one local or three non-local models. The comparison of the different approaches allows us to identify a trend, in order to obtain results in better agreement with experiment.

CuF 2 is known to be an antiferromagnetic compound with a weak ferromagnetism due to the anisotropy of its monoclinic unit cell ͑Dzialoshinsky-Moriya mechanism͒. We investigate the magnetic ordering of this compound by means of ab initio periodic unrestricted Hartree-Fock calculations and by cluster calculations which employ state-of-the-art configuration interaction expansions and modern density functional theory techniques. The combined use of periodic and cluster models permits us to firmly establish that the antiferromagnetic order arises from the coupling of one-dimensional subunits which themselves exhibit a very small ferromagnetic coupling between Cu neighbor cations. This magnetic order could be anticipated from the close correspondence between CuF 2 and rutile crystal structures. ͓S0163-1829͑99͒15301-3͔

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Ab initio calculations for electronic states of hydrazine are reported. The VUV spectrum is analyzed. The first transitions are all Rydberg transitions and the first valence states are only expected above 10 eV. The first five vertical ionization potentials are reported. The structural properties of the N2H + ion conformers are discussed.