Extension of Second-Principles Density Functional Theory into the time domain

TL;DR

This paper extends second-principles density functional theory to time-dependent simulations, enabling large-scale optical and transport property calculations for diverse materials with modest computational resources.

Contribution

The authors develop a time-dependent SPDFT method that accurately models electron dynamics in large systems, improving upon traditional approaches for metals and insulators.

Findings

SPDFT can simulate spectra of large systems like SrTiO3, diamond, and lithium.

Results in SrTiO3 are similar to linear response DFT, with improvements in diamond and lithium.

SPDFT captures electron-electron interactions, spectra, and transport properties more accurately.

Abstract

We present an extension of the second-principles density functional theory (SPDFT) method to perform time-dependent simulations. Our approach, which calculates the evolution of the density matrix in real time and real space using the Liouville-von Neumann equation of motion, allows determining optical and transport properties for very large systems, involving tens of thousands of atoms, using very modest computational platforms. In contrast with other methods, we show that SPDFT can be applied to a wide variety of materials including both metals and insulators. In particular, we illustrate its capabilities by obtaining the spectra of SrTiO$_3$, diamond and metallic lithium. We find that, while SPDFT results in SrTiO$_3$ are quite similar to those obtained from DFT using linear perturbation theory, we observe significant improvements over this method in both diamond and metallic lithium. The inclusion of electron-electron interactions during the evolution of the density matrix in diamond allows the spectra to more closely resemble those obtained with the Bethe-Salpeter equation than from perturbation theory. In lithium time-dependent SPDFT not only predicts interband transitions but also the Drude peak, opening the possibility of detailed ab initio studies of transport properties beyond many of the usual approximations.