Accurate full configuration interaction correlation energy estimates for five- and six-membered rings

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Molecular Modeling

Background:

• Accurate calculation of electronic correlation energy is crucial for predicting molecular properties.
• Previous studies have focused on smaller systems, necessitating investigation of larger ring molecules.
• The blind challenge by Eriksen et al. highlighted the need for high-accuracy benchmarks for ring systems.

Purpose of the Study:

• To compute accurate full configuration interaction (FCI) frozen-core correlation energy estimates for 12 five- and six-membered ring molecules.
• To provide benchmark FCI correlation energies using the cc-pVDZ basis set.
• To assess the performance and convergence of various single-reference quantum chemistry methods against these FCI benchmarks.

Main Methods:

• Full Configuration Interaction (FCI) calculations using an optimized-orbital selected configuration interaction approach.
• Configuration Interaction using a Perturbative Selection made Iteratively (CIPSI) algorithm.
• Calculation of correlation energies for Møller-Plesset (MP2-MP5), Coupled-Cluster (CC2-CC4, CCSD, CCSDT, CCSDTQ), and Completely Renormalized Coupled-Cluster (CR-CC(2,3)) methods.

Main Results:

• Accurate FCI correlation energy estimates with errors below 1 millihartree were obtained for 12 ring molecules.
• MP4 demonstrated a favorable accuracy/cost ratio, while MP5 showed degraded performance.
• CC3 outperformed CCSD(T) and CR-CC(2,3).
• CC4 showed slightly better accuracy than CCSDTQ, with both methods achieving results within 2 millihartree of the FCI limit.

Conclusions:

• The study provides high-accuracy FCI correlation energies for a series of important ring molecules.
• CC3 and CC4 emerge as highly accurate and efficient methods for larger systems.
• The findings offer valuable benchmarks for evaluating and developing new quantum chemistry methods.