Energetically the single sheet of graphite (graphene) is more stable than the
nanotube. The energy difference between the two systems can be directly related
to the strain energy involved in rolling up the graphene sheet to form the
nanotube. We have carried out first principle electronic structure calculations
and evaluated the strain energy as a function of the nanotube radius. The
dependence of the strain energy on the diameter of the nanotube has been found
by several groups to be welldescribed by a continuum elasticity model. We
attempt to examine why this is the case and show where atomistics enter the
description.Comment: 10 pages, 4 figure
