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

Abstract

An intermolecular potential energy surface for He 2 Br 2 complex in the ground state is calculated at the levels of fourth-order ͑MP4͒ Møller-Plesset and coupled-cluster ͓CCSD͑T͔͒ 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-Br 2 -He configuration, while the two other ones to ''police-nightstick'' and tetrahedral structures. The corresponding well depths are Ϫ90.39/ Ϫ89.18, Ϫ81.23/Ϫ80.78 and Ϫ74.40/Ϫ74.02 cm Ϫ1 , respectively, at MP4/CCSD͑T͒ levels of theory. It is found that results obtained by summing three-body parametrized HeBr 2 interactions and the He-He interaction are in very good accord with the corresponding MP4/CSSD͑T͒ configuration energies of the He 2 Br 2 . Variational calculations using a sum of three-body interactions are presented to study the bound states of the vdW He 2 Br 2 complex. The binding energy D 0 and the corresponding vibrationally averaged structure are determined for different isomers of the cluster and their comparison with the available experimental data is discussed.

Full-dimensional multi configuration time dependent Hartree calculations of the ground and vibrationally excited states of He2,3Br2 clusters

“…Reported ab initio results have been shown that for He 2 Br 2 system, the pairwise atom-atom interactions are not able to describe the PES of the complex, while a sum of threebody HeBr 2 terms, 29 plus the He-He interaction, can accurately represent the interaction energies for this cluster. 34 This latter has been also supported by recent experimental data a) Electronic mail: alvaro.v@iff.csic.es.…”

“…These findings have been found to be in accord with predictions made by previous theoretical investigations for the tetraatomic clusters. 31,34 The work presented here expands our previous efforts to evaluate the multidimensional surfaces of such vdW complexes obtained from first principles ab initio computations, by direct comparison with the experiment. In this way we can study the role of uncertainties in the PES on the spectroscopic and dynamic properties of these systems.…”

“…Recently high quality ab initio potential energy surfaces (PESs) have been calculated for such triatomic species, 20,[24][25][26][27][28][29][30] and attempts have also been made using pairwise three-body interaction potentials to represent the PESs of larger complexes. [31][32][33][34][35] Thus the first issue in this context, from the theoretical side, is how to properly describe the multidimensional potential energy surface or, in other words, at what extent the usual assumption of additive forces holds. Reported ab initio results have been shown that for He 2 Br 2 system, the pairwise atom-atom interactions are not able to describe the PES of the complex, while a sum of threebody HeBr 2 terms, 29 plus the He-He interaction, can accurately represent the interaction energies for this cluster.…”

“…39 Up to date reduced five dimensional (5D) variational calculations have been carried for the He 2 Br 2 on the PES of Ref. 34, which includes three-body terms. Also by using a semiempirical pairwise HeBr potential surface quantum-chemistry-like treatments analogous to Hartree, 37,38 configuration-interaction, 40 and full-configurationinteraction 41 calculations, in electronic structure methodology have been also reported for larger systems up to N = 60, N = 5, and N = 4, respectively.…”

Quasi-classical trajectories study of Ne2Br2(B) vibrational predissociation: Kinetics and product distributions

“…Recent studies on the structure of He 2 Br 2 and HeICl complexes 50,51 and EQM calculations on He 2 Cl 2 24 have shown that the global PES for these systems is accurately approximated by…”