7,767 research outputs found
Strengthening gold-gold bonds by complexing gold clusters with noble gases
We report an unexpectedly strong and complex chemical bonding of rare-gas
atoms to neutral gold clusters. The bonding features are consistently
reproduced at different levels of approximation within density-functional
theory and beyond: from GGA, through hybrid and double-hybrid functionals, up
to renormalized second-order perturbation theory. The main finding is that the
adsorption of Ar, Kr, and Xe reduces electron-electron repulsion within gold
dimer, causing strengthening of the Au-Au bond. Differently from the dimer, the
rare-gas adsorption effects on the gold trimer's geometry and vibrational
frequencies are mainly due to electron occupation of the trimer's lowest
unoccupied molecular orbital. For the trimer, the theoretical results are also
consistent with far-infrared multiple photon dissociation experiments.Comment: To be published in Inorganic Chemistry Communication
Big Data of Materials Science - Critical Role of the Descriptor
Statistical learning of materials properties or functions so far starts with
a largely silent, non-challenged step: the choice of the set of descriptive
parameters (termed descriptor). However, when the scientific connection between
the descriptor and the actuating mechanisms is unclear, causality of the
learned descriptor-property relation is uncertain. Thus, trustful prediction of
new promising materials, identification of anomalies, and scientific
advancement are doubtful. We analyse this issue and define requirements for a
suited descriptor. For a classical example, the energy difference of
zincblende/wurtzite and rocksalt semiconductors, we demonstrate how a
meaningful descriptor can be found systematically.Comment: Accepted to Phys. Rev. Let
Theoretical evidence for unexpected O-rich phases at corners of MgO surfaces
Realistic oxide materials are often semiconductors, in particular at elevated
temperatures, and their surfaces contain undercoordiated atoms at structural
defects such as steps and corners. Using hybrid density-functional theory and
ab initio atomistic thermodynamics, we investigate the interplay of
bond-making, bond-breaking, and charge-carrier trapping at the corner defects
at the (100) surface of a p-doped MgO in thermodynamic equilibrium with an O2
atmosphere. We show that by manipulating the coordination of surface atoms one
can drastically change and even reverse the order of stability of reduced
versus oxidized surface sites.Comment: 5 papges, 4 figure
Structure and electronic properties of transition-metal/Mg bimetallic clusters at realistic temperatures and oxygen partial pressures
Composition, atomic structure, and electronic properties of TMMgO
clusters (TM = Cr, Ni, Fe, Co, ) at realistic temperature and
partial oxygen pressure conditions are explored using the
{\em ab initio} atomistic thermodynamics approach. The low-energy isomers of
the different clusters are identified using a massively parallel cascade
genetic algorithm at the hybrid density-functional level of theory. On
analyzing a large set of data, we find that the fundamental gap E
of the thermodynamically stable clusters are strongly affected by the presence
of Mg-coordinated O moieties. In contrast, the nature of the transition
metal does not play a significant role in determining E. Using
E of a cluster as a descriptor of its redox properties, our
finding is against the conventional belief that the transition metal plays the
key role in determining the electronic and therefore chemical properties of the
clusters. High reactivity may be correlated more strongly with oxygen content
in the cluster than with any specific TM type.Comment: 7 pages, 5 figure
Charged-Surface Instability Development in Liquid Helium; Exact Solutions
The nonlinear dynamics of charged-surface instability development was
investigated for liquid helium far above the critical point. It is found that,
if the surface charge completely screens the field above the surface, the
equations of three-dimensional (3D) potential motion of a fluid are reduced to
the well-known equations describing the 3D Laplacian growth process. The
integrability of these equations in 2D geometry allows the analytic description
of the free-surface evolution up to the formation of cuspidal singularities at
the surface.Comment: latex, 5 pages, no figure
Learning physical descriptors for materials science by compressed sensing
The availability of big data in materials science offers new routes for
analyzing materials properties and functions and achieving scientific
understanding. Finding structure in these data that is not directly visible by
standard tools and exploitation of the scientific information requires new and
dedicated methodology based on approaches from statistical learning, compressed
sensing, and other recent methods from applied mathematics, computer science,
statistics, signal processing, and information science. In this paper, we
explain and demonstrate a compressed-sensing based methodology for feature
selection, specifically for discovering physical descriptors, i.e., physical
parameters that describe the material and its properties of interest, and
associated equations that explicitly and quantitatively describe those relevant
properties. As showcase application and proof of concept, we describe how to
build a physical model for the quantitative prediction of the crystal structure
of binary compound semiconductors
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