Ab initio non-covalent crystal field theory for lanthanide complexes: a multiconfigurational non-orthogonal group...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate prediction of lanthanide complex properties is crucial for materials science and catalysis.
• Existing ab initio methods face challenges in systematically describing non-covalent interactions in metal-ligand bonding.
• Lanthanide complexes exhibit unique magnetic and spectroscopic properties influenced by their electronic environment.

Purpose of the Study:

• To develop and implement a novel multiconfigurational ab initio methodology for calculating crystal field energy levels and magnetic properties of lanthanide complexes.
• To systematically incorporate non-covalent contributions to metal-ligand bonding within the theoretical framework.
• To provide a more accurate and efficient computational tool for studying lanthanide-based materials.

Main Methods:

• A two-step ab initio approach using non-orthogonal fragments.
• Optimization of separate ionic fragment wave functions (lanthanide ions, ligands) considering environmental effects.
• Reduction to an effective non-orthogonal configuration interaction (CI) problem via Löwdin-partitioning using scalar relativistic (DKH2) Hamiltonian.

Main Results:

• The proposed multiconfigurational non-orthogonal group functions (MC-NOGF) method, implemented for first-order degenerate perturbation theory, shows excellent agreement with full CAHF/CASCI-SO calculations.
• Energies and magnetic properties of 44 lanthanide complexes calculated using the MC-NOGF method closely match those from methods including metal-ligand covalency.
• The MC-NOGF approach demonstrates superior performance compared to the Fragment Ab Initio Model Potential (FAIMP) approximation for non-covalent interactions.

Conclusions:

• The developed MC-NOGF methodology effectively captures the predominantly electrostatic character of metal-ligand interactions in lanthanide complexes.
• This new ab initio approach offers a significant improvement over previous methods for describing non-covalent interactions, leading to more accurate property predictions.
• The findings pave the way for more reliable computational studies of lanthanide complexes, aiding in the design of novel materials and catalysts.