A Practical Framework for Simulating Time-Resolved Spectroscopy Based on a Real-time Dyson Expansion

TL;DR

This paper presents a scalable real-time Dyson expansion framework for simulating time-resolved spectroscopy, enabling more efficient and larger-scale non-equilibrium Green's function calculations.

Contribution

The paper introduces the theoretical foundation and scalability strategies of the RT-DE framework, advancing the simulation of dynamical many-body correlations in time-resolved spectroscopy.

Findings

Enabled simulations of larger systems beyond previous methods

Developed strategies to improve computational scalability

Outlined future directions for first-principles non-equilibrium studies

Abstract

Time-resolved spectroscopy is a powerful tool for probing electron dynamics in molecules and solids, revealing transient phenomena on sub-femtosecond timescales. The interpretation of experimental results is often enhanced by parallel numerical studies, which can provide insight and validation for experimental hypotheses. However, developing a theoretical framework for simulating time-resolved spectra remains a significant challenge. The most suitable approach involves the many-body non-equilibrium Green's function formalism, which accounts for crucial dynamical many-body correlations during time evolution. While these dynamical correlations are essential for observing emergent behavior in time-resolved spectra, they also render the formalism prohibitively expensive for large-scale simulations. Substantial effort has been devoted to reducing this computational cost -- through approximations and numerical techniques -- while preserving the key dynamical correlations. The ultimate goal is to enable first-principles simulations of time-dependent systems ranging from small molecules to large, periodic, multidimensional solids. In this perspective, we outline key challenges in developing practical simulations for time-resolved spectroscopy, with a particular focus on Green's function methodologies. We highlight a recent advancement toward a scalable framework: the real-time Dyson expansion (RT-DE). We introduce the theoretical foundation of RT-DE and discuss strategies for improving scalability, which have already enabled simulations of system sizes beyond the reach of previous fully dynamical approaches. We conclude with an outlook on future directions for extending RT-DE to first-principles studies of dynamically correlated, non-equilibrium systems.