The Simplest Possible Approach for Simulating S₀- S₁ Conical Intersections with DFT/TDDFT: Adding One Doubly Excited...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurately describing conical intersections (CIs) is crucial for understanding photoinduced molecular dynamics.
• Standard time-dependent density functional theory (TDDFT) methods often fail to reproduce the correct topology of CIs, particularly the S0-S1 CI.
• This limitation hinders the accurate simulation of bond-making and bond-breaking processes.

Purpose of the Study:

• To develop a computational method that accurately describes the topology of S0-S1 conical intersections.
• To enable the study of bond-making and bond-breaking in photoinduced dynamics.
• To provide a more reliable tool for theoretical investigations of photochemical reactions.

Main Methods:

• A novel combination of density functional theory/time-dependent density functional theory (DFT/TDDFT) and configuration interaction (CI) is presented.
• The proposed TDDFT-1D method incorporates one optimized doubly excited configuration alongside DFT/TDDFT singly excited states.
• A large configuration interaction Hamiltonian is employed within this framework.

Main Results:

• The TDDFT-1D method successfully corrects the incorrect topology of the S0-S1 conical intersection.
• Physically meaningful potential energy surfaces near S0-S1 avoided crossings are obtained for ethylene and stilbene.
• Vertical excitation energies far from the crossings remain largely unchanged.
• The method correctly reproduces the topology of the S0-S1 CI and the geometric phase for the linear water molecule.

Conclusions:

• The developed TDDFT-1D method offers a significant improvement for studying photochemical dynamics.
• It provides accurate potential energy surfaces and correctly describes the topology of conical intersections.
• This approach enhances the reliability of theoretical simulations for bond-making and bond-breaking processes in excited states.