Coupled-Cluster Density-Based Many-Body Expansion.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Coupled-cluster with singles and doubles and perturbative triples (CCSD(T)) is the gold standard for accurate molecular electronic structure calculations.
• The N^7 computational scaling of CCSD(T) severely limits its application to large molecular systems.

Purpose of the Study:

• To develop and assess a resource-efficient method for performing accurate CCSD(T) calculations on large molecular systems.
• To evaluate the performance of a density-based many-body expansion in conjunction with CCSD(T).

Main Methods:

• Application of a density-based many-body expansion method combined with CCSD(T).
• Assessment of accuracy for neutral, protonated, and deprotonated water hexamers, and (H2O)16 and (H2O)17 clusters.
• Comparison with conventional energy-based many-body expansions and investigation of density approximation effects (Hartree-Fock vs. coupled-cluster densities).

Main Results:

• A density-based two-body expansion achieved CCSD(T) energies within chemical accuracy (4 kJ/mol) for neutral water clusters.
• This accuracy surpassed that of conventional energy-based three-body expansions.
• The accuracy was maintained even when using Hartree-Fock densities instead of coupled-cluster densities.

Conclusions:

• The density-based many-body expansion offers a computationally efficient and parallelizable alternative for achieving CCSD(T)-quality results.
• This method significantly expands the feasibility of high-accuracy electronic structure calculations for large and complex molecular systems.