A double exponential coupled cluster theory in the fragment molecular orbital framework

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Fragmentation-based methods partition large chemical systems for electronic structure calculations.
• Accurate treatment of electronic correlation is crucial for large molecular systems.

Purpose of the Study:

• To develop and benchmark a dual exponential operator-based coupled cluster theory within the fragment molecular orbital (FMO) framework.
• To efficiently account for high-rank electronic correlation in large chemical systems.

Main Methods:

• Developed a dual exponential operator-based coupled cluster theory integrated with the FMO framework.
• Constructed zeroth-order reference determinants for fragments and fragment pairs using two-body FMO expansion.
• Induced dynamical correlation via fragment-specific rank-one and rank-two operators, including triple excitations through operator contractions.

Main Results:

• The proposed method achieves quantitative accuracy comparable to conventional and FMO-based coupled-cluster methods.
• Demonstrated significant reduction in computational scaling compared to traditional approaches.
• Showcased systematic improvement in accuracy with increased orbital contractions for triple excitations.

Conclusions:

• The dual exponential operator-based coupled cluster FMO method provides an accurate and computationally efficient approach for large chemical systems.
• This methodology offers a promising avenue for studying complex molecular interactions and properties.
• The accuracy is tunable, allowing for tailored calculations based on system size and desired precision.