Response properties from frozen-density embedding approximate second-order coupled-cluster theory.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Accurate calculation of molecular properties is crucial for understanding chemical phenomena.
• Existing methods like coupled cluster with singles and approximate doubles (CC2) and frozen-density embedding (FDE) have limitations for complex systems.
• There is a need for robust computational frameworks that can handle system-environment interactions.

Purpose of the Study:

• To implement and validate the coupled frozen-density embedding (FDEc) formalism for calculating ground-state and excited-state properties.
• To extend the FDEc method to linear-response properties and transition moments using the CC2 model.
• To provide an open-source implementation of FDEc within the Serenity quantum chemistry program.

Main Methods:

• Implementation of the FDEc formalism using projection-based embedding and non-additive kinetic-energy functionals.
• Utilized the resolution-of-the-identity technique for computational efficiency.
• Incorporated CC2, algebraic diagrammatic construction scheme of second order (ADC(2)), and their scaled variants.

Main Results:

• Successfully calculated excitation energies, energy splittings, and oscillator strengths for excitonically coupled dimers.
• Determined excited-state/difference dipole moments for a formaldehyde-water system.
• Accurately computed optical rotatory dispersion for a microsolvated organic chromophore, resolving limitations of uncoupled methods.

Conclusions:

• The FDEc framework accurately captures inter-subsystem couplings essential for response property calculations.
• This implementation provides a powerful tool for studying molecular aggregates and solvated systems.
• The results highlight the importance of including system-environment response couplings for accurate predictions.