  We explore the effects of geometry on the thermal conductivity (kappa) of
silicon and germanium nanowires, with lengths between 10-120 nm and diameters
up to 5-6 nm. To this end we perform molecular dynamics simulations with the
LAMMPS software, using Tersoff interatomic potentials. We consider nanowires
with polygonal cross section and we discuss the effect of the transverse
geometry on the thermal conductivity. We also consider tubular (hollow)
nanowires and core/shell combinations of Si/Ge and Ge/Si, and we compare the
heat transport of the core/shell structure with that of the separated core and
shell components.
