Projector-Based Quantum Embedding Study of Iron Complexes.

Area of Science:

• Computational chemistry
• Quantum chemistry

Background:

• Spin-crossover (SCO) complexes are crucial in materials science.
• Accurate calculation of SCO energies is computationally demanding.
• Iron-containing systems present unique challenges for electronic structure calculations.

Purpose of the Study:

• To assess the efficacy of Projection-based embedding theory (PBET) for calculating spin-crossover energies.
• To evaluate PBET's performance using various wave function and DFT methods.
• To explore PBET as a cost-effective alternative to canonical calculations for SCO complexes.

Main Methods:

• PBET was employed to embed Fe centers into frozen ligand potentials.
• MP2, CCSD, and CCSD(T) methods were embedded in SCAN and r2SCAN DFT potentials.
• Results were compared against canonical calculations and literature values.

Main Results:

• PBET calculations showed improvement over underlying DFT for most Fe-containing systems.
• PBET compensated for wave function method limitations, yielding results comparable to rigorous calculations.
• The methodology struggled with systems exhibiting spin-crossover energies near zero.

Conclusions:

• PBET presents a pragmatic and computationally less expensive approach for studying spin-crossover complexes.
• Recalculating electronic structure around the metal center within a DFT ligand field is a promising strategy.
• Further refinement is needed for systems with near-zero spin-crossover energies.