239 research outputs found
Dispersion interactions between semiconducting wires
The dispersion energy between extended molecular chains (or equivalently
infinite wires) with non-zero band gaps is generally assumed to be expressible
as a pair-wise sum of atom-atom terms which decay as . Using a model
system of two parallel wires with a variable band gap, we show that this is not
the case. The dispersion interaction scales as for large interwire
separations , as expected for an insulator, but as the band gap decreases
the interaction is greatly enhanced; while at shorter (but non-overlapping)
separations it approaches a power-law scaling given by , \emph{i.e.}
the dispersion interaction expected between \emph{metallic} wires. We
demonstrate that these effects can be understood from the increasing length
scale of the plasmon modes (charge fluctuations), and their increasing
contribution to the molecular dipole polarizability and the dispersion
interaction, as the band gaps are reduced. This result calls into question
methods which invoke locality assumptions in deriving dispersion interactions
between extended small-gap systems.Comment: 8 pages, 5 figure
Charge Transfer from Regularized Symmetry-Adapted Perturbation Theory
16 pages, 16 figure
An Efficient Illumination Invariant Tiger Detection Framework for Wildlife Surveillance
Tiger conservation necessitates the strategic deployment of multifaceted
initiatives encompassing the preservation of ecological habitats, anti-poaching
measures, and community involvement for sustainable growth in the tiger
population. With the advent of artificial intelligence, tiger surveillance can
be automated using object detection. In this paper, an accurate illumination
invariant framework is proposed based on EnlightenGAN and YOLOv8 for tiger
detection. The fine-tuned YOLOv8 model achieves a mAP score of 61% without
illumination enhancement. The illumination enhancement improves the mAP by
0.7%. The approaches elevate the state-of-the-art performance on the ATRW
dataset by approximately 6% to 7%.Comment: accepted at ICCIS 202
Molecular dynamics study of CO2 absorption and desorption in zinc imidazolate frameworks
This research utilised two high-performance computing facilities. Development of the force field was carried out using Queen Mary's MidPlus computational facilities, supported by QMUL Research-IT and funded by EPSRC grant EP/K000128/1. The molecular dynamics simulations were carried out using the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk), with access made available through our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202). MG and CY were supported by both the China Scholarship Council and Queen Mary University of London. AM was supported by a European Union Marie Sklodowska-Curie fellowship
Simulation study of pressure and temperature dependence of the negative thermal expansion in Zn(CN)(2)
12 pages, 16 figures12 pages, 16 figures12 pages, 16 figures12 pages, 16 figure
Beyond Born-Mayer: Improved Models for Short-Range Repulsion in ab Initio Force Fields
Short-range repulsion
within intermolecular force fields is conventionally
described by either Lennard-Jones (<i>A</i>/<i>r</i><sup>12</sup>) or Born–Mayer (<i>A</i> exp(−<i>Br</i>)) forms. Despite their widespread use, these simple functional
forms are often unable to describe the interaction energy accurately
over a broad range of intermolecular distances, thus creating challenges in the development of ab initio
force fields and potentially leading to decreased accuracy and transferability.
Herein, we derive a novel short-range functional form based on a simple
Slater-like model of overlapping atomic densities and an iterated
stockholder atom (ISA) partitioning of the molecular electron density.
We demonstrate that this Slater–ISA methodology yields a more
accurate, transferable, and robust description of the short-range
interactions at minimal additional computational cost compared to
standard Lennard-Jones or Born–Mayer approaches. Finally, we
show how this methodology can be adapted to yield the standard Born–Mayer
functional form while still retaining many of the advantages of the
Slater-ISA approach
From dimers to the solid-state: Distributed intermolecular force-fields for pyridine
A.A. thanks A.W.E. financial support through the EngDoc studentship from M3S Centre for Doctoral Training (EPSRC Grant No. EP/G036675/1). General computational infrastructure used is developed under No. EPSRC EP/K039229/1
Distributed Multipoles from a Robust Basis-Space Implementation of the Iterated Stockholder Atoms Procedure
The
recently developed iterated stockholder atoms (ISA) approach
of Lillestolen and Wheatley (<i>Chem. Commun.</i> <b>2008</b>, 5909) offers a powerful method for defining atoms in
a molecule. However, the real-space algorithm is known to converge
very slowly, if at all. Here, we present a robust, basis-space algorithm
of the ISA method and demonstrate its applicability on a variety of
systems. We show that this algorithm exhibits rapid convergence (taking
around 10–80 iterations) with the number of iterations needed
being unrelated to the system size or basis set used. Further, we
show that the multipole moments calculated using this basis-space
ISA method are as good as, or better than, those obtained from Stone’s
distributed multipole analysis (<i>J. Chem. Theory Comput.</i> <b>2005</b>, <i>1</i>, 1128), exhibiting better
convergence properties and resulting in better behaved penetration
energies. This can have significant consequences in the development
of intermolecular interaction models
High pressure ionic and molecular crystals of ammonia monohydrate within density functional theory
A combination of first-principles density functional theory calculations and
a search over structures predicts the stability of a proton-transfer
modification of ammonia monohydrate with space group P4/nmm. The phase diagram
is calculated with the PBE density functional, and the effects of a
semi-empirical dispersion correction, zero point motion, and finite temperature
are investigated. Comparison with MP2 and coupled cluster calculations shows
that the PBE functional over-stabilizes proton transfer phases because too much
electronic charge moves with the proton. This over-binding is partially
corrected by using the PBE0 hybrid exchange-correlation functional, which
increases the enthalpy of P4/nmm by about 0.6 eV per formula unit relative to
phase I of ammonia monohydrate (AMH-I) and shifts the transition to the proton
transfer phase from the PBE pressure of 2.8 GPa to about 10 GPa. This is
consistent with experiment as proton transfer phases have not been observed at
pressures up to ~9 GPa, while higher pressures have not yet been explored
experimentally.Comment: 10 pages, 9 figure
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