Photoabsorption spectra from adiabatically exact time-dependent density-functional theory in real time

Abstract

Photoabsorption spectra for 2-electron singlet systems are obtained from the real-time propagation of the time-dependent Kohn–Sham equations in the adiabatically exact approximation. The latter is provided by the exact ground state exchange–correlation potential corresponding to the instantaneous density. The results are compared to exact data obtained from the solution of the interacting Schrödinger equation. We find that the adiabatically exact approximation provides very good results for transitions of genuinely single excitation character but yields incorrect results if double excitations contribute substantially. However, the extent of the error can vary: some double excitations are just shifted in energy whereas others are missed completely. These situations are analyzed with the help of transition densities.