Black phosphorus is a monatomic semiconducting
layered material
that degrades exothermically in the presence of light and ambient
contaminants. Its degradation dynamics remain largely unknown. Even
before degradation, local-probe studies indicate non-negligible local
curvature—through a nonconstant height distribution—due
to the unavoidable presence of intrinsic defects. We establish that
these intrinsic defects are photo-oxidation sites because they lower
the chemisorption barrier of ideal black phosphorus (>10 eV and
out
of visible-range light excitations) right into the visible and ultraviolet
range (1.6 to 6.8 eV), thus enabling photoinduced oxidation and dissociation
of oxygen dimers. A full characterization of the material’s
shape and of its electronic properties at the early stages of the
oxidation process is presented as well. This study thus provides fundamental
insights into the degradation dynamics of this novel layered material.
SignificancePhosphorene is a new 2D atomic material, and we document a drastic reduction of its electronic gap when under a conical shape. Furthermore, geometry determines the properties of 2D materials, and we introduce discrete differential geometry to study them. This geometry arises from particle/atomic positions; it is not based on a parametric continuum, and it applies across broad disciplinary lines.
a b s t r a c tPseudopotential-based Density-Functional Theory (DFT) permits the calculation of material properties with a modest computational effort, besides an acknowledged tradeoff of generating and testing pseudopotentials that reproduce established benchmark structural and electronic properties. To facilitate the needed benchmarking process, here we present a pragmatic method to optimize pseudopotentials for arbitrary materials directly from eigenvalue sets consistent with all-electron results. This method thus represents a much needed pragmatic route for the creation and assessment of sensitive pseudopotentials for DFT calculations that has been exemplified within the context of the SIESTA code. Comprehensive optimized pseudopotentials, basis sets, and lattice parameters are provided for twenty chemical elements in the bulk, and for both LDA and GGA exchange-correlation potentials. This method helps addressing the following issues: (i) the electronic dispersion and structural properties for Ge, Pd, Pt, Au, Ag, and Ta better agree with respect to all-electron results now, (ii) we provide the expected metallic behavior of Sn in the bulk -which comes out semiconducting when using available pseudopotentials, (iii) we create a validated pseudopotential for LDA-tungsten, and (iv) we create the first Bi pseudopotential for SIESTA that reproduces well-known electron and hole pockets at the L and T points. We investigated the transferability of these pseudopotentials and basis sets, and predict a new phase for two-dimensional tin as well.
Filamentary enstatite crystals are found in interplanetary dust particles of likely cometary origin but are very rare or absent in meteorites. Crystallographic characteristics of filamentary enstatites indicate that they condensed directly from vapor. We measured the O isotopic composition of an enstatite ribbon from a giant cluster interplanetary dust particle to be δ 18 O= 25±55,which is inconsistent at the 2σ level with the composition of the Sun inferred from the Genesis solar wind measurements. The particle's O isotopic composition, consistent with the terrestrial composition, implies that it condensed from a gas of non-solar O isotopic composition, possibly as a result of vaporization of disk region enriched in 16 O-depleted solids. The relative scarcity of filamentary enstatite in asteroids compared to comets implies either that this crystal condensed from dust vaporized in-situ in the outer Solar System where comets formed, or it condensed in the inner Solar System and was subsequently transported outward to the comet-forming region.
We present in this article a pseudopotential (PP) database for DFT calculations in the context of the SIESTA code [1–3]. Comprehensive optimized PPs in two formats (psf files and input files for ATM program) are provided for 20 chemical elements for LDA and GGA exchange-correlation potentials. Our data represents a validated database of PPs for SIESTA DFT calculations. Extensive transferability tests guarantee the usefulness of these PPs.
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