An ab initio study of the intermolecular potential surfaces of HeCH4 and NeCH4

The intermolecular potential surfaces for the Van der Waals complexes HeCH4 and NeCH4 are studied by ab initio theory using complete fourth-order Møller-Plesset perturbation theory (MP4) with an efficient basis set containing bond functions. For HeCH4, the global minimum occurs at R = 3.4 Å, θ = 180°, φ = 0° (in a Jacobi coordinate system) with a minimum energy De = −26.2 cm−1. For NeCH4, the global minimum occurs at R = 3.5 Å, θ = 180°, φ = 0° with a minimum energy De = −59.0 cm−1. Two saddle points were found for each of the systems. The potential energy surfaces are compared with the semiempirical surfaces and recent ab initio results on the same systems.