A two-scale approach to electron correlation in multiconfigurational perturbation theory

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Calculating dynamic electron correlation in large molecular systems is computationally intensive.
• Accurate treatment of electron correlation is crucial for understanding molecular behavior.

Purpose of the Study:

• To develop a computationally efficient method for calculating dynamic electron correlation in large molecular systems.
• To enable accurate electronic structure calculations for complex molecules.

Main Methods:

• A new approach based on multiconfigurational second-order perturbation theory (CASPT2) is proposed.
• The method partitions the system into an active site and an environment.
• Dynamic correlation is calculated at the CASPT2 level for the active site, while the environment is treated with lower computational cost.

Main Results:

• The new method offers substantial savings in storage and computational demands compared to full CASPT2 calculations for large systems.
• Approximation introduces small errors, which are outweighed by the computational benefits.
• The scheme provides a hierarchical approach to electron correlation.

Conclusions:

• The proposed method provides a computationally feasible way to study dynamic electron correlation in large molecular systems.
• This hierarchical approach allows for treating different molecular scales with appropriate levels of theory.
• The method is particularly beneficial when static correlation is adequately handled for the entire system.