On the Simulation of Photoreactions Using Restricted Open-Shell Kohn-Sham Theory.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Theoretical Chemistry

Background:

• Describing ground-state chemical reactions using ab initio multi-electron theory is standard practice, often employing density functional theory (DFT) with molecular dynamics (MD).
• Simulating excited-state reactions computationally presents significant challenges, particularly in achieving self-consistent solutions for Kohn-Sham equations.

Purpose of the Study:

• To investigate the suitability of computational codes for simulating excited-state dynamics.
• To compare the performance of Car-Parrinello molecular dynamics and Q-Chem for excited-state reaction simulations.
• To explore applications in modeling photoreactions.

Main Methods:

• Utilized ab initio molecular dynamics (AIMD) for simulating nuclear and electronic motion.
• Employed restricted open-shell Kohn-Sham theory within the Car-Parrinello MD framework.
• Leveraged the Q-Chem code as an alternative for excited-state simulations.

Main Results:

• Identified challenges in obtaining self-consistent Kohn-Sham solutions for excited states.
• Demonstrated the application of both Car-Parrinello and Q-Chem codes to simulate excited-state molecular dynamics.
• Presented specific applications to photoreactions, showcasing the codes' capabilities.

Conclusions:

• Both Car-Parrinello and Q-Chem codes show potential for simulating excited-state dynamics.
• The study provides insights into the practical application of these methods for modeling photoreactions.
• Advances in computational methods are crucial for understanding complex excited-state processes.