Journal of Molecular Structure (Theo&em), 261 (1992) 31-54 zyxwvutsrqponmlkjihgfedcbaZYXWV Elsevier Science Publishers B.V., Amsterdam 37 zyxwvut Ab initio calculations of nonadditive effects* M.M. Szczesniak” and G. Chalasitiskibg’ ‘Department of Chemistry, Oakland University, Rochester, MI 48309 (USA) bDepartment of Chemistry and Biochemistry, Southern Illinois University, Carbondak IL 62901 (USA) (Received 21 November 1991) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ Abstract Supermolecular Meller-Plesset perturbation theory in conjunction with intermolecular Meller-Plesset perturbation theory permits the dissection of the nonadditive threebody interaction into physically meaningful contributions, such as exchange, induction, deforma- tion, and dispersion. Recently, such a partitioning has been performed for a number of trimers, such as polar ((HF),,(HCl),, (H,O),,(NH,&), nonpolar ((CH,),),and Ar-containing clusters (Ar,HCl, Ar,H,O, Ar,). The present paper attempts to compare the nonadditive properties across this wide spectrum of interacting systems. The following nonadditive terms: Heitler-London-exchange, SCF-deformation, dispersion, and second-order exchange are analysed, and their role in the overall three-body potentials is discussed. INTRODUCTION Nonadditive interactions have been the subject of intense investigations since the work of Axilrod and Teller [l]. Early studies concentrated on model systems, such as three hydrogen atoms, and the first review of the earlier results was included in the monograph by Margenau and Kestner [2]. Development of ab initio methods spurred a great deal of activity in the area of calculations of nonadditive interactions. Following the pioneering work on the trimer of water by Stillinger and co-workers [3], nonadditive properties of many chemically interesting systems were examined. The rapidly growing number of ab initio results was reviewed in the early eighties by Schuster et al. [4]. Since then, however, further advances in Correspondence to: M.M. Szczgsniak, Department of Chemistry, Oakland University, Rochester, MI 48309, USA. 1 Permanent address: Department of Chemistry, University of Warsaw, 02-993 Warsaw, Poland. *Dedicated to the memory of Professor Charles A. Coulson. 01661280/92/$05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.