Coupled cluster benchmarks of large noncovalent complexes: The L7 dataset as well as DNA-ellipticine and buckycatcher-fullerene

In this work, benchmark binding energies for dispersion-bound complexes in the L7 dataset, the DNA-ellipticine intercalation complex, and the buckycatcher-C-60 complex with 120 heavy atoms using a focal-point method based on the canonical form of second-order MOller-Plesset theory (MP2) and the domain based local pair natural orbital scheme for the coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] extrapolated to the complete basis set (CBS) limit are reported. This work allows for increased confidence given the agreement with respect to values recently obtained using the local natural orbital CCSD(T) for L7 and the canonical CCSD(T)/CBS result for the coronene dimer (C2C2PD). Therefore, these results can be considered pushing the CCSD(T)/CBS binding benchmark to the hundred-atom scale. The disagreements between the two state-of-the-art methods, CCSD(T) and fixed-node diffusion Monte Carlo, are substantial with at least 2.0 (similar to 10%), 1.9 (similar to 5%), and 10.3 kcal/mol (similar to 25%) differences for C2C2PD in L7, DNA-ellipticine, and buckycatcher-C-60, respectively. Such sizable discrepancy above chemical accuracy for large noncovalent complexes indicates how challenging it is to obtain benchmark binding interactions for systems beyond small molecules, although the three up-to-date density functionals, PBE0+D4, omega B97M-V, and B97M-V, agree better with CCSD(T) for these large systems. In addition to reporting these values, different basis sets and various CBS extrapolation parameters for Hartree-Fock and MP2 correlation energies were tested for the first time in large noncovalent complexes with the goal of providing some indications toward optimal cost effective routes to approach the CBS limit without substantial loss in quality.

Automated summary

This work reports benchmark binding energies for dispersion-bound complexes, DNA-ellipticine intercalation complex, and buckycatcher-C-60 complex with 120 heavy atoms using a focal-point method based on MP2 and CCSD(T) extrapolated to the CBS limit. The discrepancies between CCSD(T) and fixed-node diffusion Monte Carlo methods are substantial for large noncovalent complexes.