Time-Dependent Open-Quantum Approach to Two-Dimensional Electronic Spectroscopy within a GW/BSE Active Space.

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Theoretical Physics

Background:

• Accurate simulation of molecular excited states is crucial for understanding photochemical processes.
• Existing methods often lack explicit treatment of laser pulse conditions and system-environment interactions.
• Two-dimensional electronic spectroscopy (2DES) provides detailed insights into ultrafast dynamics.

Purpose of the Study:

• To develop and validate a novel theoretical and computational framework for calculating 2DES.
• To integrate first-principle electronic structure methods with open quantum system dynamics.
• To accurately model molecular systems under realistic experimental laser excitation.

Main Methods:

• Real-time propagation of the electronic wave function.
• Application of the GW/Bethe-Salpeter Equation (BSE) formalism for electronic structure.
• Incorporation of open quantum system theory and phase-cycling techniques.
• Inclusion of pure electronic dephasing in time-dependent calculations.

Main Results:

• The methodology successfully computes 2DES for benzene, chlorophyll b, and a benzene-phenol dimer.
• Calculated spectra exhibit clear signatures of stimulated emission and excited-state absorption.
• Coherence dynamics were analyzed as a function of population time, with and without dephasing.
• Results show good agreement with available experimental and theoretical data.

Conclusions:

• The presented approach accurately simulates 2DES by combining first-principle electronic structure with explicit laser pulse and dephasing effects.
• This method enhances the connection between theoretical predictions and experimental 2DES measurements.
• The framework provides a powerful tool for investigating excited-state dynamics in complex molecular systems.