Toward Full Configuration Interaction for Transition-Metal Complexes.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Transition-metal complexes are crucial in catalysis and materials science.
• Accurate calculation of their electronic properties, like singlet-triplet gaps, is computationally demanding.
• Full Configuration Interaction (FCI) provides exact results but is intractable for large systems.

Purpose of the Study:

• To develop and validate an efficient approximation to FCI for calculating singlet-triplet gaps.
• To assess the performance of the incremental FCI (iFCI) method on model transition-metal complexes.
• To improve the computational efficiency of iFCI through screening techniques.

Main Methods:

• Adaptation of the incremental FCI (iFCI) method using a many-body expansion.
• Application of iFCI to four model transition-metal complexes (Zn, V, Cu).
• Development and testing of screening techniques to reduce computational cost.

Main Results:

• iFCI significantly reduces computational cost compared to FCI.
• Screening methods decreased the number of 3-body terms by over 90% with controlled errors.
• Calculated spin gaps closely approximated experimental values for the studied complexes.
• Successfully treated a complex with 142 valence electrons and 444 active orbitals.

Conclusions:

• iFCI is an efficacious and computationally feasible approximation for FCI calculations.
• The developed screening techniques enhance the efficiency of iFCI.
• The method shows promise for accurate prediction of electronic properties in transition-metal systems.