Incorporating decoherence into solid-state time-dependent density functional theory

Abstract

Time-dependent density functional theory (TDDFT) has developed into an efficient and versatile description of realistic extended many-electron systems driven, e.g., by strong laser fields. It accounts for the fully coherent evolution of the $N$-electron wave packet representing an isolated system. Decoherence as encountered in open systems by coupling to external degrees of freedom of a bath of, e.g., phonons or defects, is, by construction, absent. In this work we present an open-quantum system (OQS) extension of TDDFT accounting for dephasing and decoherence due to electron-phonon or defect scattering. We test the OQS-TDDFT for high-harmonic generation and irreversible changes of dielectric properties in solids driven by strong ir and mid-ir laser pulses. We present applications to diamond as a prototypical wide band-gap dielectric. For weak pulses we demonstrate the equivalence of OQS-TDDFT with the solution of the Bloch equations for the reduced one-particle density matrix while differences appear at high excitation densities. Our study highlights the importance of the accurate representation of the band structure in simulations of the harmonic spectrum. Narrow avoided crossings within the Brillouin zone can give rise to Bloch-type oscillations.