  Ando's surface roughness model is applied to metallic nanowires and extended
beyond small roughness size and infinite barrier limit approximations for the
wavefunction overlaps, such as the Prange-Nee approximation. Accurate and fast
simulations can still be performed without invoking these overlap
approximations by averaging over roughness profiles using finite domain
distribution functions to obtain an analytic solution for the scattering rates.
The simulations indicate that overlap approximations, while predicting a
resistivity that agrees more or less with our novel approach, poorly estimate
the underlying scattering rates. All methods show that a momentum gap between
left- and right-moving electrons at the Fermi level, surpassing a critical
momentum gap, gives rise to a substantial decrease in resistivity.
