Time dependent vibrational electronic coupled cluster (VECC) theory for non-adiabatic nuclear dynamics

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Computational Spectroscopy

Background:

• Simulating photo-electron and UV-VIS absorption spectra requires going beyond the Born-Oppenheimer approximation for non-adiabatic vibronic models.
• Existing methods can be computationally expensive for complex systems with many degrees of freedom.

Purpose of the Study:

• To introduce and validate a novel time-dependent vibrational electronic coupled-cluster (VECC) approach.
• To enable accurate simulation of time-dependent properties and spectra for non-adiabatic vibronic systems.
• To develop a computationally efficient method with favorable scaling.

Main Methods:

• Development of a time-dependent VECC approach utilizing second-quantized bosonic operators.
• Implementation of a mixed linear and exponential ansatz for compact wave-function representation.
• The method avoids basis sets and has polynomial scaling with the number of degrees of freedom.

Main Results:

• The VECC method accurately predicts short-time dynamical properties and spectra, comparable to multi-configurational time-dependent Hartree calculations.
• Benchmark applications on small models and molecules demonstrate high accuracy.
• Successful application to a large-scale vibronic model of hexahelicene (14 electronic states, 63 normal modes).

Conclusions:

• The proposed VECC method is a powerful and efficient tool for studying non-adiabatic dynamics and spectroscopy.
• Its favorable computational cost makes it suitable for complex molecular systems.
• The approach provides accurate predictions for photo-electron and UV-VIS absorption spectra.