4,282 research outputs found
Predicting the Volumes of Crystals
New crystal structures are frequently derived by performing ionic
substitutions on known crystal structures. These derived structures are then
used in further experimental analysis, or as the initial guess for structural
optimization in electronic structure calculations, both of which usually
require a reasonable guess of the lattice parameters. In this work, we propose
two lattice prediction schemes to improve the initial guess of a candidate
crystal structure. The first scheme relies on a one-to-one mapping of species
in the candidate crystal structure to a known crystal structure, while the
second scheme relies on data-mined minimum atom pair distances to predict the
crystal volume of the candidate crystal structure and does not require a
reference structure. We demonstrate that the two schemes can effectively
predict the volumes within mean absolute errors (MAE) as low as 3.8% and 8.2%.
We also discuss the various factors that may impact the performance of the
schemes. Implementations for both schemes are available in the open-source
pymatgen software.Comment: 8 figures, 2 table
Barrettes Designed as Friction Foundations: A Case History
This paper describes the performance of a fully instrumented test barrette subjected to an ultimate loading of 30932 kN. The load transfer characteristics were measured by vibrating wire strain gauges. Rod extensometers recorded the displacements at several locations along the barrette shaft. Test results indicated that substantial loads were carried in shaft resistance. The end bearing component was reduced by poor toe conditions caused by debris accumulation at the trench base. The load - displacement behaviour and factor of safety in barrette foundation design LS discussed. The toad test results of a subsequent working barrette confirmed that the performance of the barrettes designed as friction foundations in the Old Alluvium is satisfactory
Accurate Force Field for Molybdenum by Machine Learning Large Materials Data
In this work, we present a highly accurate spectral neighbor analysis
potential (SNAP) model for molybdenum (Mo) developed through the rigorous
application of machine learning techniques on large materials data sets.
Despite Mo's importance as a structural metal, existing force fields for Mo
based on the embedded atom and modified embedded atom methods still do not
provide satisfactory accuracy on many properties. We will show that by fitting
to the energies, forces and stress tensors of a large density functional theory
(DFT)-computed dataset on a diverse set of Mo structures, a Mo SNAP model can
be developed that achieves close to DFT accuracy in the prediction of a broad
range of properties, including energies, forces, stresses, elastic constants,
melting point, phonon spectra, surface energies, grain boundary energies, etc.
We will outline a systematic model development process, which includes a
rigorous approach to structural selection based on principal component
analysis, as well as a differential evolution algorithm for optimizing the
hyperparameters in the model fitting so that both the model error and the
property prediction error can be simultaneously lowered. We expect that this
newly developed Mo SNAP model will find broad applications in large-scale,
long-time scale simulations.Comment: 25 pages, 9 figure
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