ABINITIO VAN DERWAALS POTENTIAL ENERGYSURFACES APPLICATION TO COMPLEXES OF BROMINE MOLECULE WITH HELIUM ATOMS

The additivity of the two and three-body potential energy surfaces (PES) is studied for the van der Waals (vdW) complex formed by Br₂ and two Helium atoms. First, the three-dimensional interaction potential for HeBr₂ molecule is calculated using a coupled-cluster (CCSD(T)) method. This surface shows a double-minimum topology in agreement with the available experimental data. In turn, an 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. It is found that results obtained by summing the above [CCSD(T)] three-body parameterized HeBr₂ interactions and the He–He interaction are in very good accord with the corresponding MP4/CSSD(T) configuration energies. Variational calculations using the above potential form are performed to calculate the bound states of the vdW complex and these results are compared with available experimental data.