Ab initio multiple spawning dynamics using multi-state second-order perturbation theory.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Dynamics

Background:

• Nonadiabatic effects are crucial in excited-state molecular dynamics.
• Accurate simulation of these effects requires sophisticated theoretical methods.

Purpose of the Study:

• To implement and apply the multi-state second-order perturbation theory (MS-CASPT2) within the ab initio multiple spawning (AIMS) framework.
• To investigate the excited-state dynamics of ethylene, focusing on nonadiabatic decay pathways.

Main Methods:

• Development and implementation of the AIMS-MSPT2 method for first-principles molecular dynamics.
• Efficient numerical calculation of nonadiabatic couplings requiring minimal extra energy computations.
• Application to simulate the excited-state dynamics of ethylene.

Main Results:

• Identified two primary conical intersection pathways (twisted-pyramidalized and ethylidene) responsible for ultrafast excited-state to ground-state population transfer in ethylene.
• Demonstrated that dynamic correlation significantly impacts the branching ratio between these decay pathways.
• Showed that the twisted-pyramidalized intersection pathway is favored over the ethylidene-like pathway under AIMS-MSPT2 description.

Conclusions:

• The AIMS-MSPT2 method provides a robust framework for studying nonadiabatic molecular dynamics.
• Dynamic correlation plays a critical role in determining the outcome of excited-state decay processes.
• The findings offer detailed insights into the photodynamics of ethylene, with implications for understanding similar processes in other molecules.