Photoabsorption spectra from time-dependent auxiliary density functional theory

Time-dependent auxiliary density perturbation theory (TDADPT) is extended to the calculation of excited states. The resulting time-dependent auxiliary density functional theory (TDADFT) is structurally identical to the original formulation of Casida. However, significant simplifications occur for the Coulomb and exchange-correlation response due to the underlying auxiliary density functional theory. Here, we present the working equations for TDADFT and a new implementation. Because this new parallel TDADFT implementation is particularly well suited for the calculation of large numbers of excitations, we validate it by the calculation of photoabsorption spectra. Direct comparison with experiment underlines the accuracy and reliability of TDADFT. For selected peaks of the studied polycyclic aromatic hydrocarbon spectra, the assignments of the underlying excitations are also presented. (author)