A new tutorial is available in the wiki web-page on the Floquet formalism for the calculation of non-linear response functions. Respect to the standard real-time approach Floquet formalism is much faster but at present it is limited to the independent particle approximation with or without scissor operator. In the tutorial we show how to calculate second-harmonic generation (SHG) and compare results with real-time approach.
https://www.lumen-code.org/wiki/index.php?title=SHG_from_Floquet_formulation
At present Floquet is available only in the develop branch of lumen, that can be downloaded from gitlab, but it will appear in the official version 2.x.
The method is described in this paper:
Floquet formulation of the dynamical Berry-phase approach to nonlinear optics in extended systems
Ignacio M. Alliati and Myrta Grüning, Electron. Struct. 5 017001 (2023)