Statement of need

There exists open-source code to determine the bulk thermal conductivity by solving the WTE for a static linear temperature gradient [J.Phys. Condens. Matter 35 (2023)]. Additionally, there exist closed-source implementations that solve the BTE in spatial and temporal Fourier space with arbitrary source terms using a Green’s function approach [Phys. Rev. B 104 (2021)]. Thus, we present a solver that fills the gap and supports microscopic thermal transport calculations in the WTE framework beyond the static limit. Specifically, the solver is able to capture size- and frequency-effects, including non-diffusive effects, by allowing the user to choose arbitrary source terms. By solving the WTE in spatial and temporal Fourier space, a bridge to common ultrafast and spatially patterned heating experiments is built. In particular, the frequency-domain Green’s function formulation naturally connects to ultrafast pump-probe experiments, where the heating is instantaneous and the subsequent thermal response is measured as a function of delay time [Struct. Dyn. 11 (2024)]. Spatially periodic temperature gratings used in transient thermal grating experiments are directly modelled by our approach as well [Nat. Comm. 13 (2022) and Struct. Dyn. 11 (2024)]. The approach presented here is easily generalizable and can be applied to arbitrary experimental and device geometries.