Externally Corrected CCSD with Renormalized Perturbative Triples (R-ecCCSD(T)) and the Density Matrix Renormalization...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Coupled-cluster methods are essential for accurate electronic structure calculations.
• Externally corrected coupled-cluster singles and doubles (ecCCSD) offers a balance between accuracy and computational cost.
• Incorporating triples corrections is crucial for high-fidelity predictions.

Purpose of the Study:

• To investigate the efficacy of renormalized perturbative triples correction with ecCCSD.
• To assess the performance of density matrix renormalization group (DMRG) and heat-bath CI (HCI) as external sources.
• To determine the optimal balance between computational cost and accuracy for external source calculations.

Main Methods:

• Implementation of renormalized perturbative triples correction.
• Utilizing DMRG and HCI for external source amplitudes in ecCCSD.
• Assessment of potential energy surfaces for H2O, N2, and F2.
• Application of a wave function diagnostic to characterize correlation treatment.

Main Results:

• The triples correction significantly improves ecCCSD accuracy.
• No instability was observed in renormalized triples during dissociation.
• Approximate wave functions were found to be efficient and accurate external sources.
• The study identified the domain of correlation treatable by the combined method.

Conclusions:

• Renormalized perturbative triples correction is a valuable addition to ecCCSD.
• Efficient and accurate external sources can be derived from approximate wave functions.
• The ecCCSD method with renormalized triples offers a promising approach for accurate quantum chemical calculations.