Finite temperature Green's function approach for excited state and thermodynamic properties of cool to warm dense matter

TL;DR

This paper introduces a finite-temperature Green's function method that improves excited state and thermodynamic property calculations of electronic systems, revealing new behaviors in warm dense matter regimes.

Contribution

It extends the retarded cumulant Green's function to finite temperatures, enhancing excited state predictions beyond the GW approximation for warm dense matter.

Findings

Correlation effects remain strong at high temperatures.

Spectral functions broaden and damping increases with temperature.

Many-body corrections are significant in Compton scattering at normal densities.

Abstract

We present a finite-temperature extension of the retarded cumulant Green's function for calculations of exited-state and thermodynamic properties of electronic systems. The method incorporates a cumulant to leading order in the screened Coulomb interaction $W$ and improves excited state properties compared to the $GW$ approximation of many-body perturbation theory. Results for the homogeneous electron gas are presented for a wide range of densities and temperatures, from cool to warm dense matter regime, which reveal several hitherto unexpected properties. For example, correlation effects remain strong at high $T$ while the exchange-correlation energy becomes small. In addition, the spectral function broadens and damping increases with temperature, blurring the usual quasi-particle picture. Similarly Compton scattering exhibits substantial many-body corrections that persist at normal densities and intermediate $T$. Results for exchange-correlation energies and potentials are in good agreement with existing theories and finite-temperature DFT functionals.