Solvatochromic shifts from coupled-cluster theory embedded in density functional theory

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Accurate calculation of electronic excitation energies is crucial for understanding molecular properties and reactions.
• Previous methods for modeling molecules in solution, such as frozen-density embedding, have limitations in capturing complex electronic interactions.
• Coupled-cluster (CC) theory provides high accuracy but is computationally expensive, especially for large systems or complex environments.

Purpose of the Study:

• To implement and validate a novel embedded coupled-cluster in density-functional theory (CC-in-DFT) scheme for calculating electronic excitation energies.
• To investigate the response properties of an active subsystem within a larger environment using CC-in-DFT.
• To assess the accuracy and efficiency of the CC-in-DFT method for molecules in solution compared to established methods and experimental data.

Main Methods:

• Development of a first implementation of the CC-in-DFT scheme, building upon existing frozen-density embedding frameworks.
• Application of the CC-in-DFT formalism to calculate coupled-cluster excitation energies for water and uracil in aqueous solution.
• Systematic investigation of factors influencing calculation accuracy, including basis set quality, cluster operator truncation, and density functional choice for ground-state embedding.

Main Results:

• The CC-in-DFT method yields results in good agreement with reference coupled-cluster calculations and experimental data for water and uracil.
• The accuracy of the CC-in-DFT calculations is found to be sensitive to the correlation treatment (basis set, cluster operator truncation) and the ground-state embedding (density functionals).
• The implemented scheme allows for efficient approximations in excited-state calculations without sacrificing accuracy, enabling cost-effective investigations.

Conclusions:

• The CC-in-DFT approach provides a computationally efficient and accurate first-principles method for studying environment effects on electronic excitations.
• This method makes it feasible to investigate specific interactions in complex systems at the coupled-cluster level of theory with a cost comparable to vacuum calculations.
• The CC-in-DFT scheme represents a significant advancement for theoretical spectroscopy of molecules in condensed phases.