  The Vapour-Liquid-Solid (VLS) model, which often includes a temperature
gradient (TG) across the catalytic metal particle, is often used to describe
the nucleation and growth of carbon nanostructures. Although the TG may be
important for the growth of carbon species from large metal particles,
molecular dynamics simulations show that it is not required for single-walled
carbon nanotube growth from small catalytic particles.
