57 research outputs found
Kinetics of Topological Stone-Wales Defect Formation in Single Walled Carbon
Topological Stone-Wales defect in carbon nanotubes plays a central role in
plastic deformation, chemical functionalization, and superstructure formation.
Here, we systematically investigate the formation kinetics of such defects
within density functional approach coupled with the transition state theory. We
find that both the formation and activation energies depend critically on the
nanotube chairality, diameter, and defect orientation. The microscopic origin
of the observed dependence is explained with curvature induced rehybridization
in nanotube. Surprisingly, the kinetic barrier follows an empirical
Br{\o}nsted-Evans-Polanyi type correlation with the corresponding formation
energy, and can be understood in terms of overlap between energy-coordinate
parabolas representing the structures with and without the defect. Further, we
propose a possible route to substantially decrease the kinetic activation
barrier. Such accelerated rates of defect formation are desirable in many novel
electronic, mechanical and chemical applications, and also facilitate the
formation of three-dimensional nanotube superstructures.Comment: 10 pages, Supporting information, The Journal of Physical Chemistry C
(2015
Structure, electronic properties and magnetic transition in manganese clusters
We systematically investigate the structural, electronic and magnetic
properties of Mn clusters ( 220) within the {\it ab-initio}
pseudopotential plane wave method using generalized gradient approximation for
the exchange-correlation energy. A new kind of icosahedral structural growth
has been predicted in the intermediate size range. Calculated magnetic moments
show an excellent agreement with the Stern-Gerlach experiment. A transition
from ferromagnetic to ferrimagnetic MnMn coupling takes place at 5 and
the ferrimagnetic states continue to be the ground states for the entire size
range. Possible presence of multiple isomers in the experimental beam has been
argued. No signature of non-metal to metal transition is observed in this size
range and the coordination dependence of electron localization is
discussed.Comment: 11 Pages and 9 Figures. Physical Review B (in press
Structure, reactivity and electronic properties of V-doped Co clusters
Structures, physical and chemical properties of V doped Co clusters
have been studied in detail using density functional theory based
first-principles method. We have found anomalous variation in stability of the
doped clusters with increasing V concentration, which has been nicely
demonstrated in terms of energetics and electronic properties of the clusters.
Our study explains the nonmonotonic variation in reactivity of CoV
clusters towards H molecules as reported experimentally [J. Phys. Chem.
{\bf 94}, 2744 (1990)]. Moreover, it provides useful insight into the cluster
geometry and chemically active sites on the cluster surface, which can help to
design better catalytic processes.Comment: 10 pages, 9 figures, 4 table
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