Solvent Effects on Nonadiabatic Dynamics: Ab Initio Multiple Spawning Propagated on CASPT2/xTB Potentials

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Chemical Dynamics

Background:

• Simulating nonadiabatic dynamics in solution is crucial for understanding molecular behavior.
• Accurate modeling requires incorporating solvent effects into quantum mechanical calculations.

Purpose of the Study:

• To develop and present a novel, open-source computational approach for simulating nonadiabatic dynamics in solution.
• To accurately capture the influence of solvent environments on molecular excited-state decay pathways.

Main Methods:

• Utilized the Ab Initio Multiple Spawning (AIMS) method for nuclear wavepacket propagation.
• Employed a hybrid quantum mechanical/quantum mechanical (QM/QM') scheme with CASPT2 for excited states and GFN2-xTB for embedding molecules.
• Integrated open-source software (PySpawn, OpenMolcas, xTB) and ORCA for initial condition generation.

Main Results:

• Successfully simulated the nonadiabatic dynamics of ethylene in vacuum, acetone, and chloroform.
• Demonstrated significant geometrical and electronic effects of solvents on the chromophore's decay mechanism.
• Validated the accuracy and applicability of the combined computational approach.

Conclusions:

• The presented QM/QM' AIMS approach offers a high standard of accuracy for nonadiabatic dynamics in solution.
• This open-source implementation facilitates advanced computational studies of molecular processes in condensed phases.
• Solvent interactions play a critical role in modulating excited-state decay pathways, as evidenced by the ethylene case study.