PHILIP HOGGANUniversité Blaise-Pascal, Clermont-Ferrand, FranceERKKI BRÄNDASDepartment of Quantum Chemistry, University of Uppsala, SwedenJEAN MARUANILaboratoire de Chimie Physique, CNRS and UPMC, Paris, FrancePIOTR PIECUCHMichigan State University, East Lansing, Michigan, USA andGERARDO DELGADO-BARRIOInstituto de Física Fundamental, CSIC, Madrid, Spain