First Principles Nonadiabatic Excited-State Molecular Dynamics in NWChem.

Area of Science:

• Computational chemistry
• Quantum dynamics
• Photochemistry

Background:

• Nonadiabatic molecular dynamics simulations are vital for studying photoinduced processes like energy transfer and charge separation.
• Accurate simulations require efficient algorithms and precise calculation of electronic transitions.

Purpose of the Study:

• To implement and validate the fewest-switches surface-hopping algorithm within the NWChem computational chemistry program.
• To enhance the simulation of quantum transitions between electronic states using novel derivative calculations and decoherence schemes.

Main Methods:

• Integration of the fewest-switches surface-hopping algorithm with linear-response time-dependent density functional theory (LR-TDDFT).
• Implementation of numerical and analytical schemes for derivative nonadiabatic couplings.
• Inclusion of electronic decoherence and a state reassigned unavoided crossings algorithm.

Main Results:

• Successful application of the new code to simulate the ultrafast decay of photoexcited benzene.
• Detailed analysis of potential energy surfaces, population decay timescales, and coupled vibrational coordinates for benzene.
• Investigation of photoinduced dynamics in trans-distyrylbenzene.

Conclusions:

• The developed NWChem implementation provides a robust framework for simulating nonadiabatic molecular dynamics.
• This work establishes a foundation for future advancements in simulating complex photochemical processes.
• The enhanced accuracy and efficiency pave the way for more sophisticated theoretical studies.