One and Two Dimensional Vibronic Spectra for an Exciton Dimer from Classical Trajectories

Area of Science:

• Quantum Chemistry
• Spectroscopy
• Theoretical Chemistry

Background:

• Calculating electronic spectra for systems with coupled electronic and nuclear motion is computationally challenging.
• Existing methods often struggle to accurately capture both excitonic and vibronic interactions simultaneously.

Purpose of the Study:

• To extend the semiclassical optimized mean trajectory (OMT) procedure for calculating electronic spectra of dimers.
• To incorporate excitonic and vibronic interactions within a unified semiclassical framework.

Main Methods:

• The quantum Hamiltonian was reformulated into a classical form using the Miller-Meyer-Stock-Thoss representation and taking the classical limit.
• Classical nuclear degrees of freedom and electron-nuclear coupling were added to create a classical Hamiltonian.
• Semiclassical quantization was applied via the OMT, originally for single potential surfaces and extended for electronic transitions.

Main Results:

• The extended OMT method was successfully applied to an excitonically coupled dimer.
• Semiclassical one- and two-dimensional spectra were computed.
• The results showed good agreement with quantum dynamical calculations using the hierarchical equations of motion (HEOM) method.

Conclusions:

• The semiclassical OMT procedure is an accurate and practical method for calculating electronic spectra in dimers with excitonic and vibronic coupling.
• This trajectory-based approach offers a viable alternative to computationally intensive quantum dynamical methods like HEOM.