An efficient local coupled cluster method for accurate thermochemistry of large systems

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Coupled cluster methods are highly accurate for electronic structure calculations.
• Standard methods face computational limitations for large molecular systems.
• Local approximations and density fitting are key to improving efficiency.

Purpose of the Study:

• To develop an efficient local coupled cluster method with perturbative triples (DF-LCCSD(T)).
• To reduce the computational cost of high-accuracy electronic structure calculations.
• To enable accurate calculations for larger and more complex molecules.

Main Methods:

• Implemented density fitting for two-electron integrals.
• Utilized local approximations (domain approximation) for virtual orbitals.
• Classified electron pairs (strong, close, weak, distant) for tailored treatment.
• Incorporated local second-order Møller-Plesset perturbation theory (LMP2) for weaker interactions.
• Optimized LCCSD treatment for strong pairs, accounting for >90% of correlation energy.

Main Results:

• Achieved 1-2 orders of magnitude reduction in computational effort compared to standard methods.
• Demonstrated negligible impact on accuracy with density fitting approximations.
• Showcased improved accuracy by including close pair LMP2 amplitudes.
• Achieved cubic scaling for integral evaluation and transformation, reduced to linear scaling with local density fitting.
• Attained quadratic scaling for LCCSD iterations, reducible to linear scaling.

Conclusions:

• The developed DF-LCCSD(T) method offers a significant improvement in computational efficiency for quantum chemistry.
• The method maintains high accuracy, making it suitable for large molecular systems.
• This approach paves the way for more extensive theoretical studies in chemistry and materials science.