Time-dependent density functional theory beyond the adiabatic local density approximation

TL;DR

This paper extends time-dependent density functional theory by incorporating viscoelastic effects, deriving frequency-dependent viscosity coefficients, and providing a formula for excitation linewidths, thus improving the understanding of electron fluid dynamics.

Contribution

It introduces a formalism that accounts for viscoelastic stresses beyond the adiabatic local density approximation in TDDFT, with explicit expressions for viscosity and linewidths.

Findings

Viscoelastic stresses appear in electron fluids beyond adiabatic LDA.

Frequency-dependent viscosity coefficients are microscopically derived.

An explicit formula for collective excitation linewidths is provided.

Abstract

In the current density functional theory of linear and nonlinear time-dependent phenomena, the treatment of exchange and correlation beyond the level of the adiabatic local density approximation is shown to lead to the appearance of viscoelastic stresses in the electron fluid. Complex and frequency-dependent viscosity/elasticity coefficients are microscopically derived and expressed in terms of properties of the homogeneous electron gas. As a first consequence of this formalism, we provide an explicit formula for the linewidths of collective excitations in electronic systems.