203 research outputs found
A method to computationally screen for tunable properties of crystalline alloys
Conventionally, high-throughput computational materials searches start from
an input set of bulk compounds extracted from material databases, and this set
is screened for candidate materials for specific applications. In contrast,
many functional materials, and especially semiconductors, are heavily
engineered alloys or solid solutions of multiple compounds rather than a single
bulk compound. To improve our ability to design functional materials, in this
work we propose a framework and open-source code to automatically construct
possible "alloy pairs" and "alloy systems" and detect "alloy members" from a
set of existing, experimental or calculated ordered compounds, without
requiring any additional metadata beyond their crystal structure. We provide
analysis tools to estimate stability across each alloy. As a demonstration, we
apply this framework to all inorganic materials in the Materials Project
database to create a new database of over 600,000 unique alloy pair entries
that can then be used in materials discovery studies to search for materials
with tunable properties. This new database has been incorporated into the
Materials Project website and linked with corresponding material identifiers
for any user to query and explore. Using an example of screening for p-type
transparent conducting materials, we demonstrate how using this methodology
reveals candidate material systems that might otherwise have been excluded by a
traditional screening. This work lays a foundation from which materials
databases can go beyond stoichiometric compounds, and approach a more realistic
description of compositionally tunable materials
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From Waste-Heat Recovery to Refrigeration: Compositional Tuning of Magnetocaloric Mn 1+ x Sb
High-throughput optical absorption spectra for inorganic semiconductors
An optical absorption spectrum constitutes one of the most fundamental
material characteristics, with relevant applications ranging from material
identification to energy harvesting and optoelectronics. However, the database
of both experimental and computational spectra is currently lacking. In this
study, we designed a computational workflow for the optical absorption spectrum
and integrated the simulated spectra into the Materials Project. Using
density-functional theory, we computed the frequency-dependent dielectric
function and the corresponding absorption coefficient for more than 1000 solid
compounds of varying crystal structure and chemistry. The computed spectra show
excellent agreement, as quantified by a high value of the Pearson correlation,
with experimental results when applying the band gap correction from the HSE
functional. The demonstrated calculated accuracy in the spectra suggests that
the workflow can be applied in screening studies for materials with specific
optical properties
A universal equivariant graph neural network for the elasticity tensors of any crystal system
The elasticity tensor that describes the elastic response of a material to
external forces is among the most fundamental properties of materials. The
availability of full elasticity tensors for inorganic crystalline compounds,
however, is limited due to experimental and computational challenges. Here, we
report the materials tensor (MatTen) model for rapid and accurate estimation of
the full fourth-rank elasticity tensors of crystals. Based on equivariant graph
neural networks, MatTen satisfies the two essential requirements for elasticity
tensors: independence of the frame of reference and preservation of material
symmetry. Consequently, it provides a universal treatment of elasticity tensors
for all crystal systems across diverse chemical spaces. MatTen was trained on a
dataset of first-principles elasticity tensors garnered by the Materials
Project over the past several years (we are releasing the data herein) and has
broad applications in predicting the isotropic elastic properties of
polycrystalline materials, examining the anisotropic behavior of single
crystals, and discovering new materials with exceptional mechanical properties.
Using MatTen, we have discovered a hundred new crystals with extremely large
maximum directional Young's modulus and eleven polymorphs of elemental cubic
metals with unconventional spatial orientation of Young's modulus
A representation-independent electronic charge density database for crystalline materials
In addition to being the core quantity in density functional theory, the
charge density can be used in many tertiary analyses in materials sciences from
bonding to assigning charge to specific atoms. The charge density is data-rich
since it contains information about all the electrons in the system. With
increasing utilization of machine-learning tools in materials sciences, a
data-rich object like the charge density can be utilized in a wide range of
applications. The database presented here provides a modern and user-friendly
interface for a large and continuously updated collection of charge densities
as part of the Materials Project. In addition to the charge density data, we
provide the theory and code for changing the representation of the charge
density which should enable more advanced machine-learning studies for the
broader community
High-throughput determination of Hubbard U and Hund J values for transition metal oxides via linear response formalism
DFT+U provides a convenient, cost-effective correction for the
self-interaction error (SIE) that arises when describing correlated electronic
states using conventional approximate density functional theory (DFT). The
success of a DFT+U(+J) calculation hinges on the accurate determination of its
Hubbard U and Hund's J parameters, and the linear response (LR) methodology has
proven to be computationally effective and accurate for calculating these
parameters. This study provides a high-throughput computational analysis of the
U and J values for transition metal d-electron states in a representative set
of over 2000 magnetic transition metal oxides (TMOs), providing a frame of
reference for researchers who use DFT+U to study transition metal oxides. In
order to perform this high-throughput study, an atomate workflow is developed
for calculating U and J values automatically on massively parallel
supercomputing architectures. To demonstrate an application of this workflow,
the spin-canting magnetic structure and unit cell parameters of the
multiferroic olivine LiNiPO4 are calculated using the computed Hubbard U and
Hund J values for Ni-d and O-p states, and are compared with experiment. Both
the Ni-d U and J corrections have a strong effect on the Ni-moment canting
angle. Additionally, including a O-p U value results in a significantly
improved agreement between the computed lattice parameters and experiment.Comment: 18 pages, 6 figure
Magnetism and magnetocaloric properties of CoMnCrO
CoMnCrO crystallizes as a normal spinel in the cubic space group, and the end members have been reported to display a
region of collinear ferrimagnetism as well as a low-temperature spin-spiral
state with variable coherence lengths from 3 nm to 10 nm in polycrystalline
samples. Here, we present the synthesis of the entire solid solution, and data
showing that the ferrimagnetic ordering temperature as well as the spin-spiral
lock-in temperature are tunable with the Co/Mn ratio. The peak magnetocaloric
entropy change was determined to be = -5.63 J kg K
in an applied magnetic field change of = 0 T to 5 T for the Mn
end-member at the ferrimagnetic ordering temperature. Using density functional
theory (DFT), we explore the shortcomings of the magnetic deformation proxy to
identify trends in across composition in this spinel system, and
explore future extensions of theory to address these discrepancies
The Effect of Natural Mulches on Crop Performance, Weed Suppression and Biochemical Constituents of Catnip and St. John\u27s Wort
Because of expanding markets for high-value niche crops, opportunities have increased for the production of medicinal herbs in the USA. An experiment was conducted in 2001 and 2002 near Gilbert, IA, to study crop performance, weed suppression, and environmental conditions associated with the use of several organic mulches in the production of two herbs, catnip (Nepeta cataria L.) and St. John\u27s wort (Hypericum perforatum L. ‘Helos’). Treatments were arranged in a completely randomized design and included a positive (hand-weeded) control, a negative (nonweeded) control, oat straw, a flax straw mat, and a nonwoven wool mat. Catnip plant height was significantly greater in the oat straw than the other treatments at 4 wk through 6 wk in 2001; at 4 to 8 wk in 2002, catnip plant height and width was significantly lower in the negative control compared with the other treatments. Catnip yield was significantly higher in the flax straw mat than all other treatments in 2001. In 2002, St. John\u27s wort yields were not statistically different in any treatments. All weed management treatments had significantly fewer weeds than the non-weeded rows in 2002. Total weed density comparisons in each crop from 2 yr showed fewer weeds present in the flax straw and wool mat treatments compared with positive control plots. There was no significant weed management treatment effect on the concentration of the target compounds, nepetalactone in catnip and pseudohypericin–hypericin in St. John\u27s wort, although there was a trend toward higher concentrations in the flax straw treatment
Vapor-liquid-solid growth of highly-mismatched semiconductor nanowires with high-fidelity van der Waals layer stacking
Nanobelts, nanoribbons and other quasi-one-dimensional nanostructures formed
from layered, so-called, van der Waals semiconductors have garnered much
attention due to their high-performance, tunable optoelectronic properties. For
layered alloys made from the gallium monochalcogenides GaS, GaSe, and GaTe,
near-continuous tuning of the energy bandgap across the full composition range
has been achieved in GaSe1-xSx and GaSe1-xTex alloys. Gold-catalyzed
vapor-liquid-solid (VLS) growth of these alloys yields predominantly nanobelts,
nanoribbons and other nanostructures for which the fast crystal growth front
consists of layer edges in contact with the catalyst. We demonstrate that in
the S-rich, GaS1-xTex system, unlike GaSe1-xSx and GaSe1-xTex, the Au-catalyzed
VLS process yields van der Waals nanowires for which the fast growth direction
is normal to the layers. The high mismatch between S and Te leads to
extraordinary bowing of the GaS1-xTex alloy's energy bandgap, decreasing by at
least 0.6 eV for x as small as 0.03. Calculations using density functional
theory confirm the significant decrease in bandgap in S-rich GaS1-xTex. The
nanowires can exceed fifty micrometers in length, consisting of tens of
thousands of van der Waals-bonded layers with triangular or hexagonal
cross-sections of uniform dimensions along the length of the nanowire. We
propose that the low solubility of Te in GaS results in an enhancement in Te
coverage around the Au catalyst-nanowire interface, confining the catalyst to
the chalcogen-terminated basal plane (rather than the edges) and thereby
enabling layer-by-layer, c-axis growth
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