5,820 research outputs found
Structurally Constrained Evolutionary Algorithm for the Discovery and Design of Metastable Phases
Metastable materials are abundant in nature and technology, showcasing
remarkable properties that inspire innovative materials design. However,
traditional crystal structure prediction methods, which rely solely on
energetic factors to determine a structure's fitness, are not suitable for
predicting the vast number of potentially synthesizable phases that represent a
local minimum corresponding to a state in thermodynamic equilibrium. Here, we
present a new approach for the prediction of metastable phases with specific
structural features, and interface this method with the XtalOpt evolutionary
algorithm. Our method relies on structural features that include the local
crystalline order (e.g., the coordination number or chemical environment), and
symmetry (e.g., Bravais lattice and space group) to filter the parent pool of
an evolutionary crystal structure search. The effectiveness of this approach is
benchmarked on three known metastable systems: XeN, with a two-dimensional
polymeric nitrogen sublattice, brookite TiO, and a high pressure BaH
phase that was recently characterized. Additionally, a newly predicted
metastable melaminate salt, -1 WCN, was found to possess an
energy that is lower than two phases proposed in a recent computational study.
The method presented here could help in identifying the structures of compounds
that have already been synthesized, and developing new synthesis targets with
desired properties
Producing High Concentrations of Hydrogen in Palladium via Electrochemical Insertion from Aqueous and Solid Electrolytes
Metal hydrides are critical materials in numerous technologies including
hydrogen storage, gas separation, and electrocatalysis. Here, using Pd-H as a
model metal hydride, we perform electrochemical insertion studies of hydrogen
via liquid and solid state electrolytes at 1 atm ambient pressure, and achieve
H:Pd ratios near unity, the theoretical solubility limit. We show that the
compositions achieved result from a dynamic balance between the rate of
hydrogen insertion and evolution from the Pd lattice, the combined kinetics of
which are sufficiently rapid that operando experiments are necessary to
characterize instantaneous PdHx composition. We use simultaneous
electrochemical insertion and X-ray diffraction measurements, combined with a
new calibration of lattice parameter versus hydrogen concentration, to enable
accurate quantification of the composition of electrochemically synthesized
PdHx. Furthermore, we show that the achievable hydrogen concentration is
severely limited by electrochemomechanical damage to the palladium and/or
substrate. The understanding embodied in these results helps to establish new
design rules for achieving high hydrogen concentrations in metal hydrides.Comment: 38 page
Crystal structure of Hop2-Mnd1 and mechanistic insights into its role in meiotic recombination
In meiotic DNA recombination, the Hop2-Mnd1 complex promotes Dmc1-mediated single-stranded DNA (ssDNA) invasion into homologous chromosomes to form a synaptic complex by a yet-unclear mechanism. Here, the crystal structure of Hop2-Mnd1 reveals that it forms a curved rod-like structure consisting of three leucine zippers and two kinked junctions. One end of the rod is linked to two juxtaposed winged-helix domains, and the other end is capped by extra ?-helices to form a helical bundle-like structure. Deletion analysis shows that the helical bundle-like structure is sufficient for interacting with the Dmc1-ssDNA nucleofilament, and molecular modeling suggests that the curved rod could be accommodated into the helical groove of the nucleofilament. Remarkably, the winged-helix domains are juxtaposed at fixed relative orientation, and their binding to DNA is likely to perturb the base pairing according to molecular simulations. These findings allow us to propose a model explaining how Hop2-Mnd1 juxtaposes Dmc1-bound ssDNA with distorted recipient double-stranded DNA and thus facilitates strand invasion
A Map of the Inorganic Ternary Metal Nitrides
Exploratory synthesis in novel chemical spaces is the essence of solid-state
chemistry. However, uncharted chemical spaces can be difficult to navigate,
especially when materials synthesis is challenging. Nitrides represent one such
space, where stringent synthesis constraints have limited the exploration of
this important class of functional materials. Here, we employ a suite of
computational materials discovery and informatics tools to construct a large
stability map of the inorganic ternary metal nitrides. Our map clusters the
ternary nitrides into chemical families with distinct stability and
metastability, and highlights hundreds of promising new ternary nitride spaces
for experimental investigation--from which we experimentally realized 7 new Zn-
and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity,
and covalency of solid-state bonding from the DFT-computed electron density, we
reveal the complex interplay between chemistry, composition, and electronic
structure in governing large-scale stability trends in ternary nitride
materials
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