Nonadiabatic exchange-correlation kernel for strongly correlated materials

TL;DR

This paper develops a nonadiabatic exchange-correlation kernel within TDDFT for strongly correlated materials, improving the description of excitation spectra and nonequilibrium dynamics by incorporating frequency dependence from DMFT.

Contribution

It introduces a rigorous method to calculate a frequency-dependent XC kernel using DMFT, enhancing TDDFT's accuracy for strongly correlated systems.

Findings

Nonadiabatic kernel shifts and reveals new excitation peaks in Hubbard model.

Significant differences in charge response of YTiO3 under laser pulse compared to adiabatic methods.

Electron correlations and nonadiabatic effects crucially influence spectra and dynamics.

Abstract

We formulate a rigorous method for calculating a nonadiabatic (frequency-dependent) exchange-correlation (XC) kernel required for correct description of both equilibrium and nonequilibrium properties of strongly correlated systems within Time-Dependent Density Functional Theory (TDDFT). To do so we use the expression for charge susceptibility provided by Dynamical Mean Field Theory (DMFT) for the effective multi-orbital Hubbard Model. We tested our formalism by applying it to the one-band Hubbard model: our nonadiabatic kernel leads to a significant modification of the excitation spectrum, shifting the peak that appears in adiabatic (simplified) solutions and disclosing a new one, in agreement with the DMFT solution. We also used our method to track the nonequilibrium charge-density response of a multi-orbital perovskite Mott insulator, YTiO3, to a perturbation by a femtosecond (fs) laser pulse. The results were quite different from those provided by the corresponding adiabatic formalism. These initial investigations indicate that electron-electron correlations and nonadiabatic features can significantly affect the spectrum and nonequilibrium properties of strongly correlated systems.