Non-adiabatic direct quantum dynamics using force fields: Toward solvation.

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Photochemistry

Background:

• Quantum dynamics simulations are crucial for understanding photo-excited molecules.
• Current methods struggle with scaling for larger systems and incorporating molecular environments.
• Accurate simulations are limited to small molecular systems due to computational cost.

Purpose of the Study:

• To present a novel computational approach, Force Field Quantum Dynamics (FF-QD), for large-scale, accurate simulations of photo-excited molecules.
• To address the bottlenecks of potential energy surface generation and nuclear dynamics propagation.
• To demonstrate the feasibility of including molecular environments, such as explicit solvents.

Main Methods:

• Parameterizing standard force fields to reproduce excited-state potential energy surfaces, including vibronic coupling.
• Introducing a hierarchy of approximations to the variational multi-configurational Gaussian method for nuclear dynamics.
• Combining quantum wavepacket descriptions for key degrees of freedom with classical trajectories for others (QM/MM-like approach).

Main Results:

• Developed the Force Field Quantum Dynamics (FF-QD) method, breaking simulation bottlenecks.
• Successfully parameterized force fields for excited states, enabling vibronic coupling.
• Demonstrated a scalable approach for nuclear dynamics using a hybrid quantum-classical method.

Conclusions:

• FF-QD offers a pathway to significantly larger and more accurate quantum dynamics simulations of photo-excited molecules.
• The method facilitates the inclusion of environmental effects, crucial for realistic molecular behavior.
• This approach paves the way for studying complex photochemical processes in larger systems.