  We use a phase field crystal model to generate large-scale bicrystalline and
polycrystalline single-layer hexagonal boron nitride (h-BN) samples and employ
molecular dynamics (MD) simulations with the Tersoff many-body potential to
study their heat transport properties. The Kapitza thermal resistance across
individual h-BN grain boundaries is calculated using the inhomogeneous
nonequilibrium MD method. The resistance displays strong dependence on the tilt
angle, the line tension and the defect density of the grain boundaries. We also
calculate the thermal conductivity of pristine h-BN and polycrystalline h-BN
with different grain sizes using an efficient homogeneous nonequilibrium MD
method. The in-plane and the out-of-plane (flexural) phonons exhibit different
grain size scalings of the thermal conductivity in polycrystalline h-BN and the
extracted Kapitza conductance is close to that of large-tilt-angle grain
boundaries in bicrystals.
