Stanford Institute for Materials and Energy Sciences,
SLAC National Accelerator Laboratory, Menlo Park, CA-94025, USA
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Advances in ultrafast laser spectroscopies over the last two decades have led to the development of a wide variety of experimental protocols for detailed time-domain investigations of electron dynamics in materials. Laser pulses across a wide range of intensities are now routinely deployed to drive valence- and core-level excitations that control and probe electron dynamics on femtosecond to attosecond timescales . In this context, theoretical methods going beyond a perturbative treatment of light-matter interaction are increasingly relevant for guiding experimental efforts and aiding the interpretation of complex time-resolved and/or nonlinear spectroscopies. In solid-state systems, the velocity-gauge formulation of real-time TDDFT (VG-RT-TDDFT) [2,3] has emerged as an efficient first-principles approach for describing laser-matter interactions and has been utilized within the past decade to model a number of strong-field phenomena [2,4]. I will discuss the formal framework of VG-RT-TDDFT within Kohn-Sham theory and describe recent efforts to extend this versatile approach to generalized Kohn-Sham (GKS)  theory for a unified description of valence and core electron dynamics in crystalline solids . In particular, accuracy improvements afforded by GKS theory for the description of important solid-state excitonic
effects in the time-domain will be discussed . Within this methodology, the calculation of observables relevant to time-resolved and/or nonlinear spectroscopies employing laser frequencies from the infrared to soft X-ray range will also be illustrated.
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