Molecular impurities in crystals:: (ReO4)2- Jahn-Teller ion in KCl

First density functional calculations on ReO42- molecules embedded in KCl are reported. The results on the isolated ReO42- molecule confirm the existence of a strong Jahn-Teller effect induced by the e vibrational mode and favoring a squashed D-2d tetrahedron as stable geometry, where the unpaired electron is placed in an similar to3z(2)-r(2) orbital. Calculations carried out on an 81 atom cluster reveal that the Jahn-Teller distortion in KCl is essentially the same as that for the free ReO42- molecule, which is thus in agreement with the geometry inferred from EPR data on KCI: ReO42-. Despite this fact, the Cl- --> ReO42- replacement is shown to produce outwards or inwards relaxations on close ions in the KCI lattice, whose origin is briefly discussed. (C) 2004 Wiley Periodicals, Inc.