Ab initio calculations, potential representation and vibrational dynamics of He2Br2 van der Waals complex

8 pages, 6 figures, 5 tables.-- PACS: 31.15.Ar; 34.20.Gj; 31.50.-x; 31.15.Md; 31.15.Dv; 36.40.Mr; 33.15.RyAn intermolecular potential energy surface for He2Br2 complex in the ground state is calculated at the levels of fourth-order (MP4) Møller–Plesset and coupled-cluster [CCSD(T)] approximations, using large-core pseudopotential for Br atoms and the aug-cc-pV5Z basis set for He. The surface is characterized by three minima and the minimum energy pathways through them. The global minimum corresponds to a linear He–Br2–He configuration, while the two other ones to "police-nightstick" and tetrahedral structures. The corresponding well depths are –90.39/–89.18, –81.23/–80.78 and –74.40/–74.02 cm–1, respectively, at MP4/CCSD(T) levels of theory. It is found that results obtained by summing three-body parametrized HeBr2 interactions and the He–He interaction are in very good accord with the corresponding MP4/CSSD(T) configuration energies of the He2Br2. Variational calculations using a sum of three-body interactions are presented to study the bound states of the vdW He2Br2 complex. The binding energy D0 and the corresponding vibrationally averaged structure are determined for different isomers of the cluster and their comparison with the available experimental data is discussed.This work has been supported by CICYT, Spain, Grant No. BFM 2001-2179 and by a European TMR network, Grant No. HPRN-CT-1999-00005. R.P. acknowledges a contract from the Comunidad Autónoma de Madrid, Spain.Peer reviewe