Automatized protocol and interface to simulate QM/MM time-resolved transient absorption at TD-DFT level with COBRAMM

Area of Science:

• Computational Chemistry
• Spectroscopy
• Photochemistry

Background:

• Simulating time-resolved transient absorption (TA) spectra is crucial for understanding excited-state dynamics in complex molecular systems.
• Previous computational methods were limited in their ability to handle medium-to-big sized chromophores in intricate environments.

Purpose of the Study:

• To introduce new implementations in the open-source COBRAMM software for automated TA spectra simulation.
• To enable the simulation of time-resolved TA spectra for medium-to-big chromophores in complex environments.
• To provide a user-friendly interface for setting up, running, and analyzing TA spectra simulations.

Main Methods:

• Utilized trajectory surface hopping for nonadiabatic dynamics simulations.
• Employed time-dependent density functional theory (TD-DFT) for excited states.
• Incorporated a hybrid quantum mechanics/molecular mechanics (QM/MM) scheme to model the environment.
• Developed auxiliary scripts for system setup, wavefunction overlap calculation, transition dipole moment evaluation, and data analysis.

Main Results:

• Successfully implemented an automated workflow for simulating time-resolved TA spectra.
• Enabled the simulation of excited-state absorption and stimulated emission.
• Demonstrated the capability to treat medium-to-big sized molecular systems within complex environments.

Conclusions:

• The new COBRAMM implementations significantly advance the computational accessibility of time-resolved TA spectroscopy.
• This work facilitates the study of complex photochemical and photophysical processes in previously computationally inaccessible systems.
• The automated workflow is expected to accelerate research in molecular dynamics and spectroscopy.