title: Comment on "Molecular structure and dynamics of off-center Cu(2+) ions and strongly coupled Cu(2+)-Cu(2+) pairs in BaF(2) crystals: Electron paramagnetic resonance and electron spin relaxation studies" [J. Chem. Phys. 127, 124705 (2007)].
abstract: In the recent study of Cu(2+)-doped BaF(2) Hoffmann et al. demonstrated using electron paramagnetic resonance spectroscopy that the Cu(2+) impurity experiences an off-center shift from the substitutional position and ascribe this distortion to the Jahn-Teller effect. In this comment, we propose that the off-center distortion observed for BaF(2):Cu(2+) is driven by pseudo-Jahn-Teller interactions which are qualitatively different and in competition with the usual Jahn-Teller effect. It is also stressed that off-center phenomena in a given host lattice are not necessarily enhanced by decreasing the ionic radius of the impurity.
authors.affiliation: Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Avda. de los Castros s/n, 39005 Santander, Spain. garciapa@unican.es
authors.forename: P
authors.initials: P
authors.lastname: García-Fernández
authors.forename: J A
authors.initials: JA
authors.lastname: Aramburu
authors.forename: M
authors.initials: M
authors.lastname: Moreno
authors.forename: M T
authors.initials: MT
authors.lastname: Barriuso