Wave Function Frozen-Density Embedding: Coupled Excitations.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate calculation of molecular properties is crucial for understanding chemical phenomena.
• Modeling large molecular systems presents significant computational challenges.

Purpose of the Study:

• To develop and present a computationally efficient method for calculating ground-state and excitation-energies of molecular agglomerates.
• To enable the investigation of potential energy surfaces for complex molecular systems.

Main Methods:

• Utilized a combination of the density-fitted, approximate second-order coupled-cluster singles and doubles (RICC2) method and frozen-density embedding (FDE).
• Presented working equations for RICC2 ground-state energies and approximate coupled excitation energies.
• The RICC2-in-RICC2 approach is applicable to systems decomposable into interacting molecules feasible for RICC2 calculation.

Main Results:

• Demonstrated the feasibility of quasi-ab initio correlated calculations for systems up to over one hundred atoms.
• The coupling step in the RICC2-in-RICC2 method is computationally insignificant due to efficient Coulomb integral evaluation.

Conclusions:

• The RICC2-in-RICC2 method provides an efficient and accurate approach for studying large molecular agglomerates.
• This method facilitates detailed investigations of potential energy surfaces for both ground and excited states in complex systems.