NanoBTE: Fast Iterative Solution of the Phonon Boltzmann Transport Equation for Nanoscale Heat Transport

Nanoscale heat dissipation has become a critical challenge in advanced semiconductor devices, where phonon transport can strongly deviate from the classical Fourier description owing to boundary scattering and ballistic effects. Here, we propose NanoBTE, a deterministic finite-volume solver for the non-gray phonon Boltzmann transport equation under the relaxation-time approximation. NanoBTE supports complex two- and three-dimensional geometries, band-resolved phonon properties, discrete-ordinates angular quadrature, volumetric heat generation, and multiple phonon boundary conditions, including thermalizing, diffuse, and specular reflections. To improve the efficiency of multiscale simulations, we implement both sequential and synthetic iterative schemes, with the latter coupling the microscopic phonon transport equation to a macroscopic diffusion-type temperature equation to accelerate convergence in near-diffusive regimes. Furthermore, NanoBTE adopts a band-direction task decomposition strategy, enabling efficient MPI-based CPU parallelization and GPU acceleration of the dominant sparse transport operations.

Chen, H., Lin, H.-X., Tian, X., Chen, H., Zhang, J., Yan, S., Shao, H., Wu, Y., Liu, J., and Zhang, H. (2026). "NanoBTE: Fast Iterative Solution of the Phonon Boltzmann Transport Equation for Nanoscale Heat Transport." arXiv preprint arXiv2607.03226.