21 research outputs found
Creation of crystal structure reproducing X-ray diffraction pattern without using database
When a sample's X-ray diffraction pattern (XRD) is measured, the
corresponding crystal structure is usually determined by searching for similar
XRD patterns in the database. However, if a similar XRD pattern is not found,
it is tremendously laborious to identify the crystal structure even for
experts. This case commonly happens when researchers develop novel and complex
materials. In this study, we propose a crystal structure creation scheme that
reproduces a given XRD pattern. We employed a combinatorial inverse design
method using an evolutionary algorithm and crystal morphing (Evolv&Morph)
supported by Bayesian optimization, which maximizes the similarity of the XRD
patterns between target one and those of the created crystal structures. For
sixteen different crystal structure systems with twelve simulated and four
powder target XRD patterns, Evolv&Morph successfully created crystal structures
with the same XRD pattern as the target (cosine similarity > 99% for the
simulated ones and > 96% the experimentally-measured ones). Furthermore, the
present method has merits in that it is an automated crystal structure creation
scheme, not dependent on a database. We believe that Evolv&Morph can be applied
not only to determine crystal structures but also to design materials for
specific properties.Comment: 18 pages, 5 figures, 2 tables, submitted to npjC
First-principles study on the intermediate compounds of LiBH
We report the results of the first-principles calculation on the intermediate
compounds of LiBH. The stability of LiBH and LiBH has been examined with the ultrasoft pseudopotential method based on
the density functional theory. Theoretical prediction has suggested that
monoclinic LiBH is the most stable among the candidate
materials. We propose the following hydriding/dehydriding process of LiBH
via this intermediate compound : LiBHLiBH LiH HLiH B H. The hydrogen content and enthalpy of the first
reaction are estimated to be 10 mass% and 56 kJ/mol H, respectively, and
those of the second reaction are 4 mass% and 125 kJ/mol H. They are in good
agreement with experimental results of the thermal desorption spectra of
LiBH. Our calculation has predicted that the bending modes for the
-phonon frequencies of monoclinic LiBH are lower than
that of LiBH, while stretching modes are higher. These results are very
useful for the experimental search and identification of possible intermediate
compounds.Comment: 7 pages, 5 figures, submitted to PR
First-principles prediction of high oxygen-ion conductivity in trilanthanide gallates Ln3GaO6
We systematically investigated trilanthanide gallates (Ln3GaO6) with the space group Cmc21 as oxygen-ion conductors using first-principles calculations. Six Ln3GaO6 (Ln = Nd, Gd, Tb, Ho, Dy, or Er) are both energetically and dynamically stable among 15 Ln3GaO6 compounds, which is consistent with previous experimental studies reporting successful syntheses of single phases. La3GaO6 and Lu3GaO6 may be metastable despite a slightly higher energy than those of competing reference states, as phonon calculations predict them to be dynamically stable. The formation and the migration barrier energies of an oxygen vacancy (VO) suggest that eight Ln3GaO6 (Ln = La, Nd, Gd, Tb, Ho, Dy, Er, or Lu) can act as oxygen-ion conductors based on VO. Ga plays a role of decreasing the distances between the oxygen sites of Ln3GaO6 compared with those of Ln2O3 so that a VO migrates easier with a reduced migration barrier energy. Larger oxygen-ion diffusivities and lower migration barrier energies of VO for the eight Ln3GaO6 are obtained for smaller atomic numbers of Ln having larger radii of Ln3+. Their oxygen-ion conductivities at 1000 K are predicted to have a similar order of magnitude to that of yttria-stabilized zirconia
Creation of crystal structure reproducing X-ray diffraction pattern without using database
Abstract When a sampleâs X-ray diffraction pattern (XRD) is measured, the corresponding crystal structure is usually determined by searching for similar XRD patterns in the database. However, if a similar XRD pattern is not found, it is tremendously laborious to identify the crystal structure even for experts. This case commonly happens when researchers develop novel and complex materials. In this study, we propose a crystal structure creation scheme that reproduces a given XRD pattern. We employed a combinatorial inverse design method using an evolutionary algorithm and crystal morphing (Evolv&Morph) supported by Bayesian optimization, which maximizes the similarity of the XRD patterns between target one and those of the created crystal structures. For sixteen different crystal structure systems with twelve simulated and four powder target XRD patterns, Evolv&Morph successfully created crystal structures with the same XRD pattern as the target (cosine similarity 99% for the simulated ones and >96% the experimentally measured ones). Furthermore, the present method has merits in that it is an automated crystal structure creation scheme, not dependent on a database. We believe that Evolv&Morph can be applied not only to determine crystal structures but also to design materials for specific properties
A Universal 3D Voxel Descriptor for Solid-State Material Informatics with Deep Convolutional Neural Networks
Abstract Material informatics (MI) is a promising approach to liberate us from the time-consuming Edisonian (trial and error) process for material discoveries, driven by machine-learning algorithms. Several descriptors, which are encoded material features to feed computers, were proposed in the last few decades. Especially to solid systems, however, their insufficient representations of three dimensionality of field quantities such as electron distributions and local potentials have critically hindered broad and practical successes of the solid-state MI. We develop a simple, generic 3D voxel descriptor that compacts any field quantities, in such a suitable way to implement convolutional neural networks (CNNs). We examine the 3D voxel descriptor encoded from the electron distribution by a regression test with 680 oxides data. The present scheme outperforms other existing descriptors in the prediction of Hartree energies that are significantly relevant to the long-wavelength distribution of the valence electrons. The results indicate that this scheme can forecast any functionals of field quantities just by learning sufficient amount of data, if there is an explicit correlation between the target properties and field quantities. This 3D descriptor opens a way to import prominent CNNs-based algorithms of supervised, semi-supervised and reinforcement learnings into the solid-state MI
Mechanisms of Covalent Coupling Reaction of Dibromofluoranthene on Au(111)
The
reaction mechanism of on-surface coupling of 7,10-dibromofluoranthene
(Br<sub>2</sub>FL) on Au(111) was studied on the basis of density
functional theory calculations, as a possible route for fabricating
graphene nanoribbons (GNRs) including pentagonal rings. The reaction
pathways and energy barriers of debromination, radical coupling, and
diffusion processes were investigated. The results indicate that the
reaction mechanism is substantially different for Br<sub>2</sub>FL
compared to that for the phenyl radical, which has been extensively
studied as a model system. The rate-limiting step was radical coupling
associated with the formation of a gold-metallic intermediate, which
is rarely observed on Au(111), because of steric repulsion between
the two radicals and that between the radicals and the substrate.
The energy barriers were comparable with those for cyclohexa-<i>m</i>-phenylene on Ag(111), and the reaction rate estimated
using transition state theory was consistent with the experimental
results. These results suggest that Br<sub>2</sub>FL is preferred
as a precursor of the coupling reaction to fabricate fluoranthene
polymers. Well-defined GNRs including pentagonal rings would be formed
by further cyclodehydrogenation