Ž . Chemical Physics 248 1999 161–179 www.elsevier.nlrlocaterchemphys Structure, bonding and redox properties of scandium oxide clusters, a model study J.R. Tobias Johnson a, ) , Itai Panas b a Inorganic Chemistry, Department of Chemistry, Goteborg UniÕersity, S-412 96 Goteborg, Sweden ¨ ¨ b Department of Inorganic EnÕironmental Chemistry, Chalmers UniÕersity of Technology, S-412 96 Goteborg, Sweden ¨ Received 26 April 1999 Abstract A systematic survey of scandium oxide molecules and clusters was performed by means of density functional theory Ž . DFT . Various types of scandium to oxygen bonding were characterized. Main features of the resulting menagerie of stable Ž. Ž. gas phase species are: 1 a basic Sc O molecule with rhombic structure, 2 a highly symmetric Sc O 2 2 2 3 Ž. molecule with structure and D symmetry, 3 an Sc O dimer, which is an O5Sc–O–O–Sc5O analogue to 3h 2 4 Ž. hydrogen peroxide, and 4 the most stable cluster of Sc O stoichiometry. The latter can be understood as two Sc atoms 2 4 bridged by two oxygen atoms and a peroxy unit, i.e. . Bond breaking in the peroxy bridge, forming can be used as a model for O dissociation on an early transition metal oxide surface. The 2 formation of ionic species was also investigated, and for all the oxide systems both cationic and anionic species were found to be stable. Ionization was also found to enhance the formation of cluster species. q 1999 Elsevier Science B.V. All rights reserved. 1. Introduction The chemistry of transition metals at ambient conditions is determined by the ionic and electronic conductivity, and by the chemical stability of their wx oxides 1 . In a sequence of quantum chemical stud- ies, we formulate a comprehensive and compact ) Corresponding author. E-mail: tobias.johnson@inoc.chalmers.se understanding of bonding and chemical stabilities for w x the Sc–Mn transition metal oxides 2,3 . These stud- ies explain trends in metal–oxygen bonding, and in the stability of an M–O–M bridge towards water addition. We seek local chemical information, com- plementing structural information obtained by means of crystallography, and chemical reactivity data pro- wx duced in experimental corrosion studies 4 . A series of benchmark quantum chemistry and experimental investigations by Bauschlicher, An- w xw x Ž . w x Ž . w x Ž drews et al. 5,6 , 7a for V , 7b for Cr , 7c for 0301-0104r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0301-0104 99 00249-9