  Symmetric minima of surface potential energy of a nanocatalyst act as
nucleation sites for chirally selective initial growth of single walled carbon
tubes at low temperatures. The nucleation sites are sites of maximum
coordination number of the adsorbed carbon. We show this using the five fold
symmetry of a pentagonal pyramid of an icosahedron. Initial zigzag structure
from nucleation sites results in formation of hexagons and pentagons that
result in anomalous cap formation. Possible cap lift off mechanism is
discussed.
