Kazuki Shitara

Prediction model of band gap for inorganic compounds by combination of density functional theory calculations and machine learning techniques

Machine learning techniques are applied to make prediction models of the

Machine-learning-based selective sampling procedure for identifying the low-energy region in a potential energy surface: A case study on proton conduction in oxides

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First-principles calculations of Zn-K XANES in Ca-deficient hydroxyapatite.

band gaps for 270 inorganic compounds using Kohn-Sham (KS) band gaps, cohesive energy, crystalline volume per atom, and other fundamental information of constituent elements as predictors. Ordinary least squares regression (OLSR), least absolute shrinkage and selection operator, and nonlinear support vector regression (SVR) methods are applied with two levels of predictor sets. When the KS band gap by generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) or modified Becke-Johnson (mBJ) is used as a single predictor, the OLSR model predicts the

Cytotoxicity of stoichiometric hydroxyapatites with different crystallite sizes

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Theoretical calculations of the thermodynamic stability of ionic substitutions in hydroxyapatite under an aqueous solution environment.

band gap of randomly selected test data with the root-mean-square error (RMSE) of 0.59 eV. When KS band gap by PBE and mBJ methods are used together with a set of predictors representing constituent elements and compounds, the RMSE decreases significantly. The best model by SVR yields the RMSE of 0.24 eV. Band gaps estimated in this way should be useful as predictors for virtual screening of a large set of materials.

Chemical Pressure-Induced Anion Order–Disorder Transition in LnHO Enabled by Hydride Size Flexibility

In this paper, we propose a selective sampling procedure to preferentially evaluate a potential energy surface (PES) in a part of the configuration space governing a physical property of interest. The proposed sampling procedure is based on a machine-learning method called the Gaussian process, which is used to construct a statistical model of the PES for identifying the region of interest in the configuration space. We demonstrate the efficacy of the proposed procedure for atomic diffusion and ionic conduction, specifically, the proton conduction in a well-studied proton-conducting oxide, barium zirconate

Efficient determination of alloy ground-state structures

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Accelerated Materials Design of Lithium Superionic Conductors Based on First-Principles Calculations and Machine Learning Algorithms

. The results of the demonstration study indicate that our procedure can efficiently identify the low-energy region characterizing the proton conduction in the host crystal lattice and that the descriptors used for the statistical PES model have a great influence on the performance.

ZnTaO2N: Stabilized High-Temperature LiNbO3-type Structure

The local environment of substitutional Zn(2+) in Ca-deficient hydroxyapatite (HAp) was investigated using experimental and theoretical analyses of the x-ray absorption near edge structure (XANES). For Zn-K XANES calculations, two situations of Zn(2+) were considered. One was Zn(2+) substituted for Ca sites in perfect HAp, and the other was a Ca-deficient HAp model of substitutional Zn(2+) associated with a Ca(2+) vacancy charge compensated by two protons. The model of Zn(2+) in perfect HAp did not reproduce the experimental Zn-K XANES spectrum. In contrast, the Ca-deficient HAp model agreed well with the experimental spectrum. This indicates that substitutional Zn(2+) in Ca-deficient HAp is associated with the Ca(2+) vacancy complex in HAp.

First-Principles Selection of Solute Elements for Er-Stabilized Bi2O3 Oxide-Ion Conductor with Improved Long-Term Stability at Moderate Temperatures

Abstract Hydroxyapatite (HAp) samples were synthesized by a solution reaction method followed by heat-treatments at three different temperatures. Special attention was given to optimizing the processing parameters to obtain the chemical composition near to the stoichiometry of HAp. No trace of secondary crystalline phase was found from powder X-ray diffraction in all samples. X-ray fluorescence measurements found that the Ca/P ratio was 1.68 ± 0.02, which is close to the stoichiometry of HAp, i.e., 1.67. Electron microscope observations revealed that the grain size was uniform within a sample, which was dependent on the heat treatment temperature. Dissolution rates in acid solution and cytotoxicity of the samples were measured. Tendency to decrease both the dissolution rates and the cytotoxicity with increasing crystallite size was observed. After heat-treatment at 1000 °C, the cytotoxicity of the sample was found to be minimal, which had uniaxial and faceted grains with a mean diameter of 200 nm.