Multi-level coupled cluster theory.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Coupled cluster theory is a powerful quantum chemical method for describing electron correlation.
• Accurate calculations of local molecular properties require sophisticated electron correlation treatments.
• Current methods often face computational scaling challenges for large systems.

Purpose of the Study:

• To develop a general formalism for applying different levels of coupled cluster theory to distinct molecular subsystems.
• To enable accurate and computationally efficient calculations of local molecular properties.
• To ensure the Pauli principle is satisfied across subsystem boundaries and varying correlation levels.

Main Methods:

• System partitioning using Cholesky decomposition of the one-electron Hartree-Fock density matrix.
• Defining subsystem-specific coupled cluster wave functions and solving coupled equations.
• Developing associated response theory for the multi-level coupled cluster formalism.

Main Results:

• A novel multi-level coupled cluster theory formalism was successfully developed.
• The method allows for seamless division of molecular systems, even across chemical bonds.
• Proof-of-principle applications demonstrated the formalism's viability and potential.

Conclusions:

• The developed multi-level coupled cluster theory provides a pathway to achieve size-intensive complexity.
• This formalism is essential for accurate and efficient computation of local molecular properties.
• It offers a significant advancement in computational quantum chemistry for complex systems.