The structure of sodium electrosodalite was determined at 20K by using synchrotron powder diffraction methods. The electron density was calculated by using a periodic unrestricted Hartree-Fock approach, and was analyzed by using topological methods. The F center was found to manifest itself as a maximum in the electron density at a non-nuclear position. It possessed a separate identity, and behaved quantum-mechanically as an open system which was bounded by a surface of local zero flux in the gradient vector-field of the electron density. Various basis sets were considered, and the introduction of a basis set which was capable of describing the F center led to a large drop in the total energy. The F center contained almost only an unpaired electron density, which was loosely bound and exhibited a very low kinetic energy density.

F Center in Sodium Electrosodalite as a Physical Manifestation of a Non-Nuclear Attractor in the Electron Density. G.K.H.Madsen, C.Gatti, B.B.Iversen, L.Damjanovic, G.D.Stucky, V.I.Srdanov: Physical Review B, 1999, 59[19], 12359-69