Effects of strong electron-electron correlations and memory in materials and time-dependent density-functional theory: recent progress and challenges*

Charge correlations play an important role in the static and dynamical properties of many materials, for example in the optical response of systems excited by short laser pulses. Because of the involvement of a number of atomistic processes that define the response of the system,  ab initio tools are needed to characterize them. Time-Dependent Density-Functional Theory (TDDFT) is an excellent choice, provided one has an appropriate exchange-correlation (XC) potential that accurately accounts for electron-electron and other charge correlations. Until very recent years, such potentials were not available. In this presentation, we first summarize our TDDFT approach for strongly correlated materials [1], in which a nonadiabatic XC potential is derived from the charge susceptibility (linear response) and electron self-energy (nonlinear response) obtained from the Dynamical Mean-Field Theory solution of an effective Hubbard model. We present results of application of the approach to types of materials: Mott insulators and a transition metal. We demonstrate how the effects of charge correlations and memory are revealed in the nonhomogeneous ultrafast metallization of VO_2,[2] demagnetization of Ni [1] and melting of the antiferromagnetic order in V₂O₃. We discuss how these ultrafast processes reveal themselves in the emission spectra of the materials and the challenges that lie ahead for the treatment of strong perturbations.

References

[1] S.R. Acharya, V. Turkowski, G. P. Zhang, and T.S. Rahman, Phys. Rev. Lett. 125, 017202 (2020).

[2] J. M. Galicia-Hernandez, V. Turkowski, G. Hernandez-Cocoletzi and T.S. Rahman,  J. Phys.: Condens. Matter 32, 20LT01 (2020).