Local time-correlation approach for calculations of x-ray spectra

We present a local time-correlation function method for real-time calculations of core level x-ray spectra (RTXS). The approach is implemented in a local orbital basis using a Crank-Nicolson time-evolution algorithm applied to an extension of the SIESTA code, together with projector augmentedwave (PAW) atomic transition matrix elements. Our RTXS is formally equivalent to Delta SCF (Delta self consistent field) Fermi's golden rule calculations with a screened core-hole and an effective independent particle approximation. Illustrative calculations are presented for several molecular and condensed matter systems and found to be in good agreement with experiment. The method can also be advantageous compared to conventional frequency-space methods.