Ab initio computations close to the one‐particle basis set limit on the weakly bound van der Waals complexes benzene–neon and benzene–argon

The equilibrium geometries and binding energies of the van der Waals (vdW) complexes benzene–neon and benzene–argon have been calculated at the level of second‐order Mo/ller–Plesset perturbation theory (MP2). Terms linear in the interelectronic distances r₁₂ were used in the MP2 treatment to converge fast to the one‐particle basis set limit. This new method, MP2‐R12 as implemented in the sore program, was applied with high quality basis sets derived from Dunning’s aug‐cc‐pVXZ (X=D,T,Q,5) sets. In reward of the efforts to reach the basis set limit, it is found that the calculated binding energies for the vdW complexes were computed virtually free of a basis set superposition error (BSSE). The key MP2‐R12 results are D_e=154 cm⁻¹ and r_e=3.32 Å for benzene–neon and D_e=553 cm⁻¹ and r_e=3.41 Å for benzene–argon. The permanent dipole moments of the vdW complexes have been computed by finite field perturbation theory. Coupled‐cluster calculations of type CCSD(T), although performed with considerably smaller basis sets than the MP2‐R12 calculations, show that, to improve the MP2‐R12 results, it is inevitable to consider correlation effects due to connected triple excitations which go beyond the MP2 description.