title: Can undoped calcium tetraborides exist? An answer from the comparison of its density functional theory electronic structure with that of rare-earth metal tetraboride.
abstract: Periodic density functional theory calculations are used to discuss the existence of metal tetraborides MB4 with divalent metals. Tetraborides which contain metal atoms inserted in a three-dimensional boron network made of B6 octahedra and B2 dumbbells exhibit a pseudo energy gap for a count of 60 valence electrons per M4(B6)2(B2)2 formula unit. Such a count satisfies the stability electron requirement for B6(2-) (20 electrons) octahedra and B2(2-) (8 electrons) units and allows the filling of two supplementary low-lying bands deriving from the valence metallic d atomic orbitals. This favored electron count is not reached for CaB4 which is then formally deficient by one electron per metal atom. This indicates that CaB4 is unlikely to exist without n-doping.
authors.affiliation: Sciences Chimiques de Rennes, UMR 6226 CNRS-ENSC Rennes-Universite de Rennes 1, Avenue du General Leclerc, F-35042 Rennes Cedex, France.
authors.forename: Mouna
authors.initials: M
authors.lastname: Ben Yahia
authors.forename: Olaf
authors.initials: O
authors.lastname: Reckeweg
authors.forename: Régis
authors.initials: R
authors.lastname: Gautier
authors.forename: Joseph
authors.initials: J
authors.lastname: Bauer
authors.forename: Thomas
authors.initials: T
authors.lastname: Schleid
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Halet
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Saillard