  Controlling heat flow at the nanoscales is pivotal to several applications,
including thermal energy harvesting and heat management. However, engineering
nanostructures is challenging because phonon-boundary interaction, not
contemplated by Fourier's law, must be taken into account. Nondiffusive models,
such as the Boltzmann transport equation (BTE), have been successfully employed
to capture size effects in complex structures; however, their widespread has
been hindered by the limited offer of open-source solvers in this space. We
fill this void by introducing OpenBTE, an efficient solver for the steady-state
phonon BTE in multidimensional structures. This tool is interfaced to
first-principles calculations, thus it unlocks the calculations of
thermal-related properties with no fitting-parameters. As an example, we employ
OpenBTE to compute the temperature and flux maps, as well as the mode-resolved,
effective thermal conductivity of Si membranes with infinite and finite
thickness. By unlocking fast nanoscale heat transport simulations, OpenBTE may
help accelerate the design of nanomaterials for thermal energy applications.
