Download Tight-binding molecular dynamics simulation study of carbon

Tight-binding molecular dynamics simulation
study of carbon nanomaterials
Gun-Do Lee a, Cai-Zhuang Wang b, Euijoon Yoon a, Nongmoon Hwang a,
and Kai-Ming Ho b
a
Department of Materials Science and Engineering, Seoul National University, Seoul, Korea
b
Department of Physics and Astronomy, Iowa State University, Ames, IA, USA
Carbon nanomaterials, such as carbon nanotubes (CNTs), fullerenes, graphene, nanoporous carbons, and nano-diamonds, have been objects attracting tremendous attention
due to their applicability for energy storage, nano-electromechanic devices, gas
sensing, and drug delivery materials for recent decades. Various simulation methods
have been used to study structural and electronic properties of carbon nanomaterials.
Among them, ab initio and classical molecular dynamics (MD) simulations have been
continuously performed to investigate carbon nanomaterials. Even if ab initio method
is very accurate, it is very expensive and takes long time. Classical MD simulation
methods have been sometimes found to be insufficient in describing properties of
nanoscale materials. In order to overcome weak points of both methods, tight-binding
method has been attempted. Environment-dependent tight binding (EDTB) method
gives accurate results on a level comparable to ab initio calculation about diamond and
amorphous carbon materials. We modified the original EDTB carbon potential by
incorporating an angle dependence factor into the repulsive energy to describe
correctly native defects in CNTs and graphene layers. Recently, we performed tightbinding molecular dynamics (TBMD) simulation by using modified EDTB carbon
potential to study vacancy reconstruction in CNTs and graphene and evaporation
processes at graphene nanoribbon (GNR) edges. In this study, we found that a double
vacancy in graphene is reconstructed into a 555-777 composed of triple pentagons and
triple heptagons which has been confirmed by a recent experiment [1]. Pentagonheptagon (5-7) pairs are found to play an important role in the reconstruction of
vacancy in CNTs. In the TBMD simulation of GNR, we found the evaporation of
carbon atoms from both the zigzag and armchair edges is preceded by the formation of
heptagon rings, which serve as a gateway for carbon atoms to escape. In the
simulation for a GNR armchair-zigzag-armchair junction, carbon atoms are
evaporated row-by-row from the outermost row of the zigzag edge, which is in
excellent agreement with recent experiments [1,2]. These results can be applied to
nano-electronic devices fabrication through the temperature-controlled edge structure
of GNR.
[1] C. O. Girit et al. Science 323, 1705 (2009)
[2] X. Jia et al. Science 323, 1701 (2009)