Time-Dependent Density Functional Theory for Open Quantum Systems with Unitary Propagation

TL;DR

This paper extends time-dependent density functional theory to open quantum systems, allowing environmental effects to be incorporated into simulations with a new bath functional, demonstrated on a helium model.

Contribution

It generalizes the Runge-Gross theorem for open systems and introduces a Markovian bath functional compatible with existing real-time codes.

Findings

The extended theorem applies to Markovian and non-Markovian systems.

A practical bath functional inspired by nonlinear Schrödinger equations is proposed.

Numerical results on a helium model demonstrate the method's effectiveness.

Abstract

We extend the Runge-Gross theorem for a very general class of Markovian and non-Markovian open quantum systems under weak assumptions about the nature of the bath and its coupling to the system. We show that for Kohn-Sham (KS) Time-Dependent Density Functional Theory, it is possible to rigorously include the effects of the environment within a bath functional in the KS potential, thus placing the interactions between the particles of the system and the coupling to the environment on the same footing. A Markovian bath functional inspired by the theory of nonlinear Schrodinger equations is suggested, which can be readily implemented in currently existing real-time codes. Finally, calculations on a helium model system are presented.