  The thermoelectric properties of two typical SiGe nanotubes are investigated
using a combination of density functional theory, Boltzmann transport theory,
and molecular dynamics simulations. Unlike carbon nanotubes, these SiGe
nanotubes tend to have gear-like geometry, and both the (6, 6) and (10, 0)
tubes are semiconducting with direct band gaps. The calculated Seebeck
coefficients as well as the relaxation time of these SiGe nanotubes are
significantly larger than those of bulk thermoelectric materials. Together with
smaller lattice thermal conductivity caused by phonon boundary and alloy
scattering, these SiGe nanotubes can exhibit very good thermoelectric
performance. Moreover, there are strong chirality and temperature dependence of
the ZT values, which can be optimized to 4.9 at room temperature and further
enhanced to 5.4 at 400 K for the armchair (6, 6) tube.
