Microscopic and macroscopic Maxwell-TDDFT descriptions for light-matter interaction in thin materials

We present a comprehensive theoretical framework for interaction of an ultrashort light pulse with a thin material based on the time-dependent density functional theory (TDDFT). We introduce a microscopic description solving the Maxwell equations for the light electromagnetic fields and the time-dependent Kohn-Sham equation for the electron dynamics simultaneously in the time domain on a common real-space grid. This scheme can simulate the light-matter interaction in thin films irrespective of the film thickness and the light intensity. For two limiting cases of extremely thin and sufficiently thick films, we develop approximate schemes. For the former, a 2D macroscopic description is developed: 2D response functions are introduced for a weak field, while time evolution equation is derived for an intense field. For the latter, the 3D macroscopic description coincides with the ordinary electromagnetism with the 3D bulk response functions for a weak field, or the multiscale Maxwell-TDDFT scheme for a strong field, which our group developed previously. In this talk, we show results for Si thin films and discuss the applicability of the microscopic and macroscopic descriptions.