An overview on potential energy surfaces of rare-gas dihalogen van der Waals clusters

In this review we report on interaction potential surface calculations of Rg–XY (Rg = rare gas and X, Y = halogens) van der Waals (vdW) complexes. Experimental data available on the structure and dynamics of such systems mainly originate from the B← X excitation spectroscopy and, therefore, potential surfaces for both electronic states involved are required for the theoretical treatments. Hence, ab initio technology is used at the coupled-cluster (CCSD(T)) level of theory for constructing these surfaces. Relativistic effects are included with the use of large-core pseudo-potentials for the halogen atoms, while efficient augmented correlation-consistent polarized basis sets are employed for the Rg ones, to ensure saturation in interaction energies in the highest level of electron correlation treatment. For all ground state Rg–dihalogen systems studied, the potential surface shows minima for both linear and T-shaped orientations. In contrast, the potential surfaces of the electronically B excited state complexes present T-shaped minimum. Variational calculations for both electronic potentials are performed to calculate the bound states of the ground and B excited vdW complexes, and binding energies, vibrationally averaged structures and spectral shifts are determined. Here, an application of the present methodology on the ground X and B excited HeI2 conformers is reported and the obtained results are discussed in terms of available experimental data. PACS numbers: 31.15.Ar, 31.50.Bc, 31.50.Df, 33.15.Fm, 33.20.Vq, 36.40.Mr