  We investigate vibration modes and their Raman activity of single-walled
carbon nanotubes that are bent within their intrinsic elastic limits. By
implementing novel boundary conditions for density-functional based
tight-binding, and using non-resonant bond polarization theory, we discover
that Raman activity can be induced by bending. Depending on the degree of
bending, high-energy Raman peaks change their positions and intensities
significantly. These effects can be explained by migration of nodes and
antinodes along tube circumference. We discuss the challenge of associating the
predicted spectral changes with experimental observations.
