6 research outputs found
Robust Superlubricity in Graphene/<i>h</i>‑BN Heterojunctions
The sliding energy landscape of the heterogeneous graphene/<i>h</i>-BN interface is studied by means of the registry index.
For a graphene flake sliding on top of <i>h</i>-BN, the
anisotropy of the sliding energy corrugation with respect to the misfit
angle between the two naturally mismatched lattices is found to reduce
with the flake size. For sufficiently large flakes, the sliding energy
corrugation is expected to be at least an order of magnitude lower
than that obtained for matching lattices regardless of the relative
interlayer orientation. Therefore, in contrast to the case of the
homogeneous graphene interface where flake reorientations are known
to eliminate superlubricty, here, a stable low-friction state is expected
to occur. Our results mark heterogeneous layered interfaces as promising
candidates for dry lubrication purposes
Interlayer Potential for Homogeneous Graphene and Hexagonal Boron Nitride Systems: Reparametrization for Many-Body Dispersion Effects
A new
parametrization of the anisotropic interlayer potential for
hexagonal boron nitride (<i>h</i>-BN ILP) is presented.
The force-field is benchmarked against density functional theory calculations
of several dimer systems within the Heyd-Scuseria-Ernzerhof hybrid
density functional approximation, corrected for many-body dispersion
effects. The latter, more advanced method for treating dispersion,
is known to produce binding energies nearly twice as small as those
obtained with pairwise correction schemes, used for an earlier ILP
parametrization. The new parametrization yields good agreement with
the reference calculations to within ∼1 and ∼0.5 meV/atom
for binding and sliding energies, respectively. For completeness,
we present a complementary parameter set for homogeneous graphitic
systems. Together with our previously suggested ILP parametrization
for the heterogeneous graphene/<i>h</i>-BN junction, this
provides a powerful tool for consistent simulation of the structural,
mechanical, tribological, and heat transport properties of both homogeneous
and heterogeneous layered structures based on graphene and <i>h</i>-BN
Smallest Archimedean Screw: Facet Dynamics and Friction in Multiwalled Nanotubes
We
identify a new material phenomenon, where minute mechanical
manipulations induce pronounced global structural reconfigurations
in faceted multiwalled nanotubes. This behavior has strong implications
on the tribological properties of these systems and may be the key
to understand the enhanced interwall friction recently measured for
boron-nitride nanotubes with respect to their carbon counterparts.
Notably, the fast rotation of helical facets in these systems upon
coaxial sliding may serve as a nanoscale Archimedean screw for directional
transport of physisorbed molecules
Interlayer Potential for Graphene/<i>h</i>‑BN Heterostructures
We present a new
force-field potential that describes the interlayer
interactions in heterojunctions based on graphene and hexagonal boron
nitride (<i>h</i>-BN). The potential consists of a long-range
attractive term and a short-range anisotropic repulsive term. Its
parameters are calibrated against reference binding and sliding energy
profiles for a set of finite dimer systems and the periodic graphene/<i>h</i>-BN bilayer, obtained from density functional theory using
a screened-exchange hybrid functional augmented by a many-body dispersion
treatment of long-range correlation. Transferability of the parametrization
is demonstrated by considering the binding energy of bulk graphene/<i>h</i>-BN alternating stacks. Benchmark calculations for the
superlattice formed when relaxing the supported periodic heterogeneous
bilayer provide good agreement with both experimental results and
previous computational studies. For a free-standing bilayer we predict
a highly corrugated relaxed structure. This, in turn, is expected
to strongly alter the physical properties of the underlying monolayers.
Our results demonstrate the potential of the developed force-field
to model the structural, mechanical, tribological, and dynamic properties
of layered heterostructures based on graphene and <i>h</i>-BN
Ultrahigh Torsional Stiffness and Strength of Boron Nitride Nanotubes
We report the experimental and theoretical study of boron
nitride
nanotube (BNNT) torsional mechanics. We show that BNNTs exhibit a
much stronger mechanical interlayer coupling than carbon nanotubes
(CNTs). This feature makes BNNTs up to 1 order of magnitude stiffer
and stronger than CNTs. We attribute this interlayer locking to the
faceted nature of BNNTs, arising from the polarity of the B–N
bond. This property makes BNNTs superior candidates to replace CNTs
in nanoelectromechanical systems (NEMS), fibers, and nanocomposites
M-Chem: a modular software package for molecular simulation that spans scientific domains
We present a new software package called M-Chem that is designed from scratch in C++ and parallelised on shared-memory multi-core architectures to facilitate efficient molecular simulations. Currently, M-Chem is a fast molecular dynamics (MD) engine that supports the evaluation of energies and forces from two-body to many-body all-atom potentials, reactive force fields, coarse-grained models, combined quantum mechanics molecular mechanics (QM/MM) models, and external force drivers from machine learning, augmented by algorithms that are focused on gains in computational simulation times. M-Chem also includes a range of standard simulation capabilities including thermostats, barostats, multi-timestepping, and periodic cells, as well as newer methods such as fast extended Lagrangians and high quality electrostatic potential generation. At present M-Chem is a developer friendly environment in which we encourage new software contributors from diverse fields to build their algorithms, models, and methods in our modular framework. The long-term objective of M-Chem is to create an interdisciplinary platform for computational methods with applications ranging from biomolecular simulations, reactive chemistry, to materials research.</p