High level ab initio study of intermolecular potential for the Rg-HX (Rg = He, Ne; X = F, Cl, Br) complexes -: III.: He-HBr

The potential energy surfaces of ground state of He -HBr complex have been calculated at several levels of theory, including the single and double excitation coupled-cluster method with noniterative perturbation treatment of triple excitation CCSD(T). Calculations have been performed using the augmented correlation-consistent polarized quadruple zeta basis set (aug-cc-pVQZ). Using the complete basis set (CBS), the global minimum with a well depth of approximately 28.792 cm(-1) has been found for the linear He-H-Br geometry (theta = 0.0degrees) with the distance R between the He atom and the center of mass of the HBr molecule equal to 0.407 nm. In addition to the global minimum, there is a second minimum at R = 0.343 nm and theta = 180degrees (a well depth of 35.707 cm(-1)). Finally the effects of the basis sets and theoretical methods on the intermolecular potential are discussed and a simple analytic form employing 17 adjustable parameters for fitting to the calculated PES is given.