Complete basis set limit ofAb initiobinding energies and geometrical parameters for various typical types of complexes

Using basis-set extrapolation schemes for a given data set, we evaluated the binding energies and geometries at the complete basis set (CBS) limit at the levels of the second order Møller-Plesset perturbation theory (MP2) and the coupled cluster theory with singles, doubles, and perturbative triples excitations CCSD(T). The systems include the hydrogen bonding (water dimer), aromatic interaction (benzene dimer), pi-H interaction (benzene-water), cation-water, anion-water, pi-cation interaction (cation-benzene), and pi-anion interaction (anion-triazine). One extrapolation method is to exploit both BSSE-corrected and BSSE-uncorrected binding energies for the aug-cc-pVNZ (N = 2, 3, 4, ...) basis set in consideration that both binding energies give the same CBS limit (CBS(B)). Another CBS limit (CBS(C)) is to use the commonly known extrapolation approach to exploit that the electron correlation energy is proportional to N(-3). Since both methods are complementary, they are useful for estimating the errors and trend of the asymptotic values. There is no significant difference between both methods. Overall, the values of CBS(C) are found to be robust because of their consistency. However, for small N (in particular, for N = 2, 3), CBS(N)(B) is found to be slightly better for water-water interactions and cation-water and cation-benzene interactions, whereas CBS(N)(C) is found to be more reliable for bezene-water and anion-water interactions. We also note that the MP2 CBS limit value based on N = 2 and 3 combined with the difference between CCSD(T) and MP2 at N = 2 would be exploited to obtain a CCSD(T)/CBS value for aromatic-aromatic interactions and anion-pi interactions, but not for cationic complexes.