Towards reliable and efficient modeling of [Cu₂O₂]²⁺-based compound electronic structures with the partially fixed...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate modeling of complex electronic structures is crucial for understanding chemical reactivity.
• Copper-oxygen complexes, particularly the [Cu2O2]2+ moiety, are vital in various catalytic processes.
• Existing computational methods often struggle with the computational cost of accurately describing these systems.

Purpose of the Study:

• To develop and validate a computationally efficient approach for modeling [Cu2O2]2+ electronic structures.
• To investigate the role of d-shell occupations in the electronic structure of [Cu2O2]2+ systems.
• To establish a protocol for predicting the properties of related complexes and designing new functional materials.

Main Methods:

• Application of the Partially Fixed Reference Space (PFRS) protocol to minimize active space size.
• Utilizing PFRS-crafted active spaces for multi-reference coupled cluster, configuration interaction, and perturbation theory calculations.
• Comparison with Density Matrix Renormalization Group (DMRG) calculations for validation.

Main Results:

• The ground-state electronic structure of [Cu2O2]2+ is dominated by d9/d10 occupations.
• Qualitative modeling of the bare [Cu2O2]2+ core is achievable with small active spaces (CAS(2,2)PFRS).
• Quantitative agreement with high-level calculations requires larger active spaces (CAS(4,4)) and MRCCSD corrections.

Conclusions:

• The PFRS protocol offers a reliable and computationally efficient method for modeling [Cu2O2]2+ systems.
• This approach enables accurate prediction of electronic structures and properties for ammonia-coordinated complexes.
• The findings facilitate the rational design of new ligands with tailored oxidative properties based on calculated d-occupancy energy gaps.