Spin-Forbidden Reactions: Adiabatic Transition States Using Spin-Orbit Coupled Density Functional Theory

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Reaction Mechanisms

Background:

• Spin-forbidden reactions involve changes in electronic spin states, complicating mechanistic studies.
• These reactions occur across multiple potential energy surfaces (PESs), unlike typical reactions on a single PES.
• Traditional methods like minimum energy crossing points (MECPs) are not stationary, posing challenges for accurate analysis.

Purpose of the Study:

• To present a novel computational approach for studying spin-forbidden reactions.
• To investigate the mechanism of spin-forbidden reactions in gold chemistry using this new method.
• To compare the efficacy of spin-orbit coupling (SOC) approaches with MECP calculations.

Main Methods:

• Utilizing the spin-orbit ZORA Hamiltonian within the density functional theory (DFT) framework.
• Calculating transition states (TS SOC) and activation free energies on a single adiabatic PES.
• Performing calculations for molecular oxygen addition to gold(I)-hydride complexes and N2O/N2Se dissociation.

Main Results:

• Successfully incorporated spin-orbit coupling (SOC) effects into DFT calculations for gold chemistry.
• Demonstrated that the SOC approach allows for the calculation of transition states and activation energies.
• Provided a comparative analysis of MECP and TS SOC methods, highlighting the accuracy of the SOC approach.

Conclusions:

• The spin-orbit coupling (SOC) approach, using spin-orbit ZORA/DFT, provides an accurate and feasible method for studying spin-forbidden reaction mechanisms.
• This methodology offers significant advantages over traditional MECP calculations for understanding complex reaction pathways.
• The findings have implications for understanding and designing reactions in gold chemistry and other systems involving spin-forbidden processes.