Relativistic real-time time dependent density functional theory for valence and core level attosecond transient absorption spectroscopy

We present fundamental insights on pure electron dynamics captured by pump–probe attosecond transient absorption processes, within the realms of relativistic real–time time-dependent density functional theory [1-3], where both scalar and spin-orbit relativistic effects are included variationally using modern atomic mean-field eXact two-component (amfX2C) Hamiltonian [4]. We address how this technique records the signature of the transient dynamics triggered by the pump pulse imprinted onto the molecular response to probe pulse, including effects of additional degrees of freedom (pump pulse features and pump–probe time delay) absent in conventional spectroscopy. Non-equilibrium response theory will be used to lend further interpretation of the simulated spectral features. Furthermore, the necessity to incorporate relativistic corrections for simulating L-edge x-ray absorption processes are showcased by comparing spectra obtained with non-relativistic, amfX2C and Dirac-Coulomb Hamiltonian.