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 Moller-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 De=154 cm-1 and r e=3.32 Å for benzene-neon and De=553 cm-1 and re=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. © 1994 American Institute of Physics.