69,893 research outputs found
Reactive Force Field for Proton Diffusion in BaZrO3 using an empirical valence bond approach
A new reactive force field to describe proton diffusion within the
solid-oxide fuel cell material BaZrO3 has been derived. Using a quantum
mechanical potential energy surface, the parameters of an interatomic potential
model to describe hydroxyl groups within both pure and yttrium-doped BaZrO3
have been determined. Reactivity is then incorporated through the use of the
empirical valence bond model. Molecular dynamics simulations (EVB-MD) have been
performed to explore the diffusion of hydrogen using a stochastic thermostat
and barostat whose equations are extended to the isostress-isothermal ensemble.
In the low concentration limit, the presence of yttrium is found not to
significantly influence the diffusivity of hydrogen, despite the proton having
a longer residence time at oxygen adjacent to the dopant. This lack of
influence is due to the fact that trapping occurs infrequently, even when the
proton diffuses through octahedra adjacent to the dopant. The activation energy
for diffusion is found to be 0.42 eV, in good agreement with experimental
values, though the prefactor is slightly underestimated.Comment: Corrected titl
Analytical calculation of pressure for confined atomic and molecular systems using the eXtreme-Pressure Polarizable Continuum Model
We show that the pressure acting on atoms and molecular systems within the
compression cavity of the eXtreme-Pressure Polarizable Continuum method can be
expressed in terms of the electron density of the systems and of the
Pauli-repulsion confining potential. The analytical expression holds for
spherical cavities as well as for cavities constructed from van der Waals
spheres of the constituting atoms of the molecular systems
Real-Time Description of the Electronic Dynamics for a Molecule close to a Plasmonic Nanoparticle
The optical properties of molecules close to plasmonic nanostructures greatly
differ from their isolated molecule counterparts. To theoretically investigate
such systems in a Quantum Chemistry perspective, one has to take into account
that the plasmonic nanostructure (e.g., a metal nanoparticle - NP) is often too
large to be treated atomistically. Therefore, a multiscale description, where
the molecule is treated by an ab initio approach and the metal NP by a lower
level description, is needed. Here we present an extension of one such
multiscale model [Corni, S.; Tomasi, J. {\it J. Chem. Phys.} {\bf 2001}, {\it
114}, 3739] originally inspired by the Polarizable Continuum Model, to a
real-time description of the electronic dynamics of the molecule and of the NP.
In particular, we adopt a Time-Dependent Configuration Interaction (TD CI)
approach for the molecule, the metal NP is described as a continuous dielectric
of complex shape characterized by a Drude-Lorentz dielectric function and the
molecule- NP electromagnetic coupling is treated by an equation-of-motion (EOM)
extension of the quasi-static Boundary Element Method (BEM). The model includes
the effects of both the mutual molecule- NP time-dependent polarization and the
modification of the probing electromagnetic field due to the plasmonic
resonances of the NP. Finally, such an approach is applied to the investigation
of the light absorption of a model chromophore, LiCN, in the presence of a
metal NP of complex shape.Comment: This is the final peer-reviewed manuscript accepted for publication
of an open access article published under an ACS AuthorChoice License, which
permits copying and redistribution of the article or any adaptations for
non-commercial purposes. Link to the original article:
http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b1108
Anisotropic-cyclicgraphene: A new two-dimensional semiconducting carbon allotrope
Potentially new, single-atom thick semiconducting 2D-graphene-like material,
called Anisotropic-cyclicgraphene, have been generated by the two stage
searching strategy linking molecular and ab initio approach. The candidate
derived from the evolutionary based algorithm and molecular simulations was
then profoundly analysed using first-principles density functional theory from
the structural, mechanical, phonon, and electronic properties point of view.
The proposed polymorph of graphene (rP16-P1m1) is mechanically, dynamically,
and thermally stable and can be semiconducting with a direct band gap of 0.829
eV.Comment: 15 pages, 14 figure
A Complex Chemical Potential: Signature of Decay in a Bose-Einstein Condensate
We explore the zero-temperature statics of an atomic Bose-Einstein condensate
in which a Feshbach resonance creates a coupling to a second condensate
component of quasi-bound molecules. Using a variational procedure to find the
equation of state, the appearance of this binding is manifest in a collapsing
ground state, where only the molecular condensate is present up to some
critical density. Further, an excited state is seen to reproduce the usual
low-density atomic condensate behavior in this system, but the molecular
component is found to produce an underlying decay, quantified by the imaginary
part of the chemical potential. Most importantly, the unique decay rate
dependencies on density () and on scattering length () can be measured in experimental tests of this theory.Comment: 4 pages, 1 figur
Vibrational signature of a single water molecule adsorbed on Pt(111): toward a reliable anharmonic description
In this study, we present a thorough benchmarking of our direct anharmonic vibrational variation-perturbation approach for adsorbed molecules on surfaces. We then use our method to describe the vibrational structure of a water molecule adsorbed on a Pt(111) surface and compare our results with the available experimental data. By using an explicitly correlated hybrid method to describe the molecule-surface interaction, we improve on the initial periodic PBE/DZP potential energy landscape and obtain vibrational frequencies that are of near-experimental accuracy. We introduce an implementation of anharmonic z-polarized IR intensity calculation and explain the absence of antisymmetric O-H stretch in the experimental data for the adsorbed water molecule, while the symmetric O-H stretch is predicted to be visible
A continuum treatment of growth in biological tissue: The coupling of mass transport and mechanics
Growth (and resorption) of biological tissue is formulated in the continuum
setting. The treatment is macroscopic, rather than cellular or sub-cellular.
Certain assumptions that are central to classical continuum mechanics are
revisited, the theory is reformulated, and consequences for balance laws and
constitutive relations are deduced. The treatment incorporates multiple
species. Sources and fluxes of mass, and terms for momentum and energy transfer
between species are introduced to enhance the classical balance laws. The
transported species include: (\romannumeral 1) a fluid phase, and
(\romannumeral 2) the precursors and byproducts of the reactions that create
and break down tissue. A notable feature is that the full extent of coupling
between mass transport and mechanics emerges from the thermodynamics.
Contributions to fluxes from the concentration gradient, chemical potential
gradient, stress gradient, body force and inertia have not emerged in a unified
fashion from previous formulations of the problem. The present work
demonstrates these effects via a physically-consistent treatment. The presence
of multiple, interacting species requires that the formulation be consistent
with mixture theory. This requirement has far-reaching consequences. A
preliminary numerical example is included to demonstrate some aspects of the
coupled formulation.Comment: 29 pages, 11 figures, accepted for publication in Journal of the
Mechanics and Physics of Solids. See journal for final versio
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