# Time-dependent coupled cluster theory on the Keldysh contour for non-equilibrium systems

## TL;DR

This paper extends finite temperature coupled cluster theory using the Keldysh formalism to study non-equilibrium thermal systems, enabling detailed simulations of driven quantum systems with applications to models like Hubbard and silicon under ultrafast pulses.

## Contribution

The authors develop and implement a Keldysh coupled cluster method for non-equilibrium, finite-temperature quantum systems, expanding the applicability of coupled cluster techniques.

## Key findings

- Successfully applied to Hubbard model with Peierls phase
- Demonstrated capability on warm-dense silicon under XUV pulse
- Extended coupled cluster theory to non-equilibrium thermal conditions

## Abstract

We leverage the Keldysh formalism to extend our implementation of finite temperature coupled cluster theory [\textit{J. Chem. Theory Comput.} 2018, \textit{14}, 5690-5700] to thermal systems that have been driven out of equilibrium. The resulting Keldysh coupled cluster theory is discussed in detail. We describe the implementation of the equations necessary to perform Keldysh coupled cluster singles and doubles calculations of finite temperature dynamics, and we apply the method to some simple systems including a Hubbard model with a Peierls phase and an {\it ab initio} model of warm-dense silicon subject to an ultrafact XUV pulse.