Ab Initio Modeling of MultiWall: A General Algorithm First Applied to Carbon Nanotubes

A general, versatile
and automated computational algorithm to design
any type of multiwall nanotubes of any chiralities is presented for
the first time. It can be applied to rolling up surfaces obtained
from cubic, hexagonal, and orthorhombic lattices. Full exploitation
of the helical symmetry permits a drastic reduction of the computational
cost and therefore opens to the study of realistic systems. As a test
case, the structural, electronic, mechanical, and transport properties
of multiwall carbon nanotubes (MWCNT) are calculated using a density
functional theory approach, and results are compared with those of
the corresponding layered (graphene-like) precursors. The interaction
between layers has a general minimum for the inter-wall distance of
≈3.4 Å, in good agreement with experimental and computed
optimal distances in graphene sheets. The metallic armchair and semiconductor
zigzag MWCNT are almost isoenergetic and their stability increases
as the number of walls increases. The vibrational fingerprint provides
a reliable tool to identify the chirality and the thickness of the
nanostructures. Finally, some promising thermoelectric features of
the semiconductor MWCNT are reproduced and discussed.