2,865 research outputs found
Studies of fullerenes and carbon nanotubes by an extended bond order potential
We present a novel approach to combine bond order potentials with long-range nonbond interactions. This extended bond order potential consistently takes into account bond terms and nonbond terms. It not only captures the advantages of the bond order potentials (i.e. simulating bond forming and breaking), but also systematically includes the nonbond contributions to energy and forces in studying the structure and dynamics of covalently bonded systems such as graphite, diamond, nanotubes, fullerenes and hydrocarbons, in their crystal and melt forms. Using this modified bond order potential, we studied the structure and thermal properties (including thermal conductivity) of C60 crystal, and the elastic properties and plastic deformation processes of the single-walled and double-walled nanotubes. This extended bond order potential enables us to simulate large deformations of a nanotube under tensile and compressive loads. The basic formulation in this paper is transferable to other bond order potentials and traditional valence force fields
Chemical functionalization of graphene
Experimental and theoretical results on chemical functionalization of
graphene are reviewed. Using hydrogenated graphene as a model system, general
principles of the chemical functionalization are formulated and discussed. It
is shown that, as a rule, 100% coverage of graphene by complex functional
groups (in contrast with hydrogen and fluorine) is unreachable. A possible
destruction of graphene nanoribbons by fluorine is considered. The
functionalization of infinite graphene and graphene nanoribbons by oxygen and
by hydrofluoric acid is simulated step by step.Comment: 13 pages, 11 figures. Invited paper for J. Phys. Cond. Mater.
"Graphene" special issue. References added, typos correcte
Site-dependent hydrogenation on graphdiyne
Graphene is one of the most important materials in science today due to its
unique and remarkable electronic, thermal and mechanical properties. However in
its pristine state, graphene is a gapless semiconductor, what limits its use in
transistor electronics. In part due to the revolution created by graphene in
materials science, there is a renewed interest in other possible graphene-like
two-dimensional structures. Examples of these structures are graphynes and
graphdiynes, which are two-dimensional structures, composed of carbon atoms in
sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two
acetylenic groups) were recently synthesized and some of them are intrinsically
nonzero gap systems. These systems can be easily hydrogenated and the relative
level of hydrogenation can be used to tune the band gap values. We have
investigated, using fully reactive molecular dynamics (ReaxFF), the structural
and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes.
Our results showed that the hydrogen bindings have different atom incorporation
rates and that the hydrogenation patterns change in time in a very complex way.
The formation of correlated domains reported to hydrogenated graphene is no
longer observed in graphdiyne cases.Comment: Submitted to Carbo
Boron Fullerenes: A First-Principles Study
A family of unusually stable boron cages was identified and examined using
first-principles local density functional method. The structure of the
fullerenes is similar to that of the B12 icosahedron and consists of six
crossing double-rings. The energetically most stable fullerene is made up of
180 boron atoms. A connection between the fullerene family and its precursors,
boron sheets, is made. We show that the most stable boron sheets are not
necessarily precursors of very stable boron cages. Our finding is a step
forward in the understanding of the structure of the recently produced boron
nanotubes.Comment: 10 pages, 4 figures, 1 tabl
Magnetically operated nanorelay based on two single-walled carbon nanotubes filled with endofullerenes Fe@C20
Structural and energy characteristics of the smallest magnetic endofullerene
Fe@C20 have been calculated using the density functional theory approach. The
ground state of Fe@C20 is found to be a septet state, and the magnetic moment
of Fe@C20 is estimated to be 8 Bohr magnetons. Characteristics of an (8,8)
carbon nanotube with a single Fe@C20 inside are studied in the framework of the
semiempirical approach. The scheme of a magnetic nanorelay based on
cantilevered nanotubes filled with magnetic endofullerenes is elaborated. The
proposed nanorelay is turned on as a result of bending of nanotubes by a
magnetic force. Operational characteristics of such a nanorelay based on (8,8)
and (21,21) nanotubes fully filled with Fe@C20 are estimated and compared to
the ones of a nanorelay made of a (21,21) nanotube fully filled with
experimentally observed (Ho3N)@C80 with the magnetic moment of 21 Bohr
magnetons. Room temperature operation of (21,21) nanotube based nanorelays is
shown.Comment: 18 pages, 9 figure
Dimensionality of Carbon Nanomaterials Determines the Binding and Dynamics of Amyloidogenic Peptides: Multiscale Theoretical Simulations
Experimental studies have demonstrated that nanoparticles can affect the rate of protein self-assembly, possibly interfering with the development of protein misfolding diseases such as Alzheimer's, Parkinson's and prion disease caused by aggregation and fibril formation of amyloid-prone proteins. We employ classical molecular dynamics simulations and large-scale density functional theory calculations to investigate the effects of nanomaterials on the structure, dynamics and binding of an amyloidogenic peptide apoC-II(60-70). We show that the binding affinity of this peptide to carbonaceous nanomaterials such as C60, nanotubes and graphene decreases with increasing nanoparticle curvature. Strong binding is facilitated by the large contact area available for π-stacking between the aromatic residues of the peptide and the extended surfaces of graphene and the nanotube. The highly curved fullerene surface exhibits reduced efficiency for π-stacking but promotes increased peptide dynamics. We postulate that the increase in conformational dynamics of the amyloid peptide can be unfavorable for the formation of fibril competent structures. In contrast, extended fibril forming peptide conformations are promoted by the nanotube and graphene surfaces which can provide a template for fibril-growth
In situ Characterization of Nanoparticles Using Rayleigh Scattering
We report a theoretical analysis showing that Rayleigh scattering could be
used to monitor the growth of nanoparticles under arc discharge conditions. We
compute the Rayleigh scattering cross sections of the nanoparticles by
combining light scattering theory for gas-particle mixtures with calculations
of the dynamic electronic polarizability of the nanoparticles. We find that the
resolution of the Rayleigh scattering probe is adequate to detect nanoparticles
as small as C60 at the expected concentrations of synthesis conditions in the
arc periphery. Larger asymmetric nanoparticles would yield brighter signals,
making possible to follow the evolution of the growing nanoparticle population
from the evolution of the scattered intensity. Observable spectral features
include characteristic resonant behaviour, shape-dependent depolarization
ratio, and mass-dependent line shape. Direct observation of nanoparticles in
the early stages of growth with unobtrusive laser probes should give insight on
the particle formation mechanisms and may lead to better-controlled synthesis
protocols
- …