Ryosuke Akashi
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View article: Can machines learn density functionals? Past, present, and future of ML in DFT
Can machines learn density functionals? Past, present, and future of ML in DFT Open
Density functional theory has become the world's favorite electronic structure method, and is routinely applied to both materials and molecules. Here, we review recent attempts to use modern machine-learning to improve density functional a…
View article: Assessing the possible superconductivity in doped perovskite hydride KMgH$_3$: Effects of lattice anharmonicity and spin fluctuations
Assessing the possible superconductivity in doped perovskite hydride KMgH$_3$: Effects of lattice anharmonicity and spin fluctuations Open
The superconducting properties of uniformly hole-doped perovskite hydride KMgH$_3$ with varying doping concentration and lattice parameter corresponding to different pressures were investigated from first principles. The superconducting tr…
View article: Hydrodynamic simulation of laser ablation with electronic entropy effects included
Hydrodynamic simulation of laser ablation with electronic entropy effects included Open
In this paper, we present a methodology of laser ablation simulation including electronic entropy effects. Ablation by ultrashort laser pulses is suitable for micromachining because of its small thermal damage. To further enhance its effec…
View article: Illuminating the Bragg intersections as roots of Dirac nodal lines and high-order van Hove singularities
Illuminating the Bragg intersections as roots of Dirac nodal lines and high-order van Hove singularities Open
We theoretically reexamine nearly uniform electron models with weak crystalline potentials. In particular, we theorize the modulation of the plane-wave branches at linear regions where multiple Bragg planes intersect. Any such linear inter…
View article: Illuminating the Bragg intersections as roots of Dirac nodal lines and high-order van Hove singularities
Illuminating the Bragg intersections as roots of Dirac nodal lines and high-order van Hove singularities Open
We theoretically reexamine nearly uniform electron models with weak crystalline potentials. In particular, we theorize the modulation of the plane-wave branches at linear regions where multiple Bragg planes intersect. Any such linear inter…
View article: Semiconducting Electronic Structure of the Ferromagnetic Spinel $\mathbf{Hg}\mathbf{Cr}_2\mathbf{Se}_4$ Revealed by Soft-X-Ray Angle-Resolved Photoemission Spectroscopy
Semiconducting Electronic Structure of the Ferromagnetic Spinel $\mathbf{Hg}\mathbf{Cr}_2\mathbf{Se}_4$ Revealed by Soft-X-Ray Angle-Resolved Photoemission Spectroscopy Open
We study the electronic structure of the ferromagnetic spinel $\mathrm{Hg}\mathrm{Cr}_2\mathrm{Se}_4$ by soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) and first-principles calculations. While a theoretical study has predi…
View article: Lattice dielectric properties of rutile $\mathrm{TiO}_2$: First-principles anharmonic self-consistent phonon study
Lattice dielectric properties of rutile $\mathrm{TiO}_2$: First-principles anharmonic self-consistent phonon study Open
We calculate the lattice dielectric function of strongly anharmonic rutile $\mathrm{TiO}_2$ from ab initio anharmonic lattice dynamics methods. Since an accurate calculation of the $Γ$ point phonons is essential for determining optical pro…
View article: Density functional theory
Density functional theory Open
Density functional theory (DFT) is an essential building block for modern theoretical physics, chemistry, and engineering, especially those concerning electronic properties. Through decades of development, various program packages for firs…
View article: A Noise-Robust Data Assimilation Method for Crystal Structure Prediction Using Powder Diffraction Intensity
A Noise-Robust Data Assimilation Method for Crystal Structure Prediction Using Powder Diffraction Intensity Open
Crystal structure prediction for a given chemical composition has long been a challenge in condensed-matter science. We have recently shown that experimental powder X-ray diffraction (XRD) data are helpful in a crystal structure search usi…
View article: Development of exchange-correlation functionals assisted by machine learning
Development of exchange-correlation functionals assisted by machine learning Open
With the recent rapid progress in the machine-learning (ML), there have emerged a new approach using the ML methods to the exchange-correlation functional of density functional theory. In this chapter, we review how the ML tools are used f…
View article: Missing quantum number of Floquet states
Missing quantum number of Floquet states Open
We reformulate the Floquet theory for periodically driven quantum systems\nfollowing a perfect analogy with the proof of Bloch theorem. We observe that\nthe current standard method for calculating the Floquet eigenstates by the\nquasi-ener…
View article: Revisiting homogeneous electron gas in pursuit of properly normed <i>ab initio</i> Eliashberg theory
Revisiting homogeneous electron gas in pursuit of properly normed <i>ab initio</i> Eliashberg theory Open
We address an issue of how to accurately include the self energy effect of\nthe screened electron-electron Coulomb interaction in the phonon-mediated\nsuperconductors from first principles. In the Eliashberg theory for\nsuperconductors, se…
View article: Roadmap on Machine learning in electronic structure
Roadmap on Machine learning in electronic structure Open
In recent years, we have been witnessing a paradigm shift in computational materials science. In fact, traditional methods, mostly developed in the second half of the XXth century, are being complemented, extended, and sometimes even compl…
View article: Machine-learning-based exchange correlation functional with physical asymptotic constraints
Machine-learning-based exchange correlation functional with physical asymptotic constraints Open
Density functional theory is the standard theory for computing the electronic structure of materials, which is based on a functional that maps the electron density to the energy. However, a rigorous form of the functional is not known and …
View article: Machine-Learning-Based Exchange-Correlation Functional with Physical Asymptotic Constraints
Machine-Learning-Based Exchange-Correlation Functional with Physical Asymptotic Constraints Open
Density functional theory is the standard theory for computing the electronic structure of materials, which is based on a functional that maps the electron density to the energy. However, a rigorous form of the functional is not known and …
View article: Chemical physics of superconductivity in layered yttrium carbide halides from first principles
Chemical physics of superconductivity in layered yttrium carbide halides from first principles Open
We perform a thorough first-principles study on superconductivity in yttrium\ncarbide halide Y$_2$$X_2$C$_2$ ($X$=Cl, Br, I) whose maximum transition\ntemperature ($T_{\\rm c}$) amounts to $\\sim$10 K. A detailed analysis on the\noptimized…
View article: Anomalous High‐Temperature Superconductivity in YH<sub>6</sub>
Anomalous High‐Temperature Superconductivity in YH<sub>6</sub> Open
Pressure‐stabilized hydrides are a new rapidly growing class of high‐temperature superconductors, which is believed to be described within the conventional phonon‐mediated mechanism of coupling. Here, the synthesis of one of the best‐known…
View article: Effect of spin fluctuations on superconductivity in V and Nb: A first-principles study
Effect of spin fluctuations on superconductivity in V and Nb: A first-principles study Open
We study the superconductivity in typical $d$-band elemental superconductors\nV and Nb with the recently developed non-empirical computational scheme based\non the density functional theory for superconductors. The effect of\nferromagnetic…
View article: First Principles Study of the Optical Dipole Trap for Two-Dimensional Excitons in Graphane
First Principles Study of the Optical Dipole Trap for Two-Dimensional Excitons in Graphane Open
Recent studies on excitons in two-dimensional materials have been widely conducted for their potential usages for novel electronic and optical devices. Especially, sophisticated manipulation techniques of quantum degrees of freedom of exci…
View article: Defining a well-ordered Floquet basis by the average energy
Defining a well-ordered Floquet basis by the average energy Open
At the moment, the most efficient method to compute the state of a\nperiodically driven quantum system is using Floquet theory and the Floquet\neigenbasis. The wide application of this basis set method is limited by: a lack\nof unique orde…
View article: Completing density functional theory by machine learning hidden messages from molecules
Completing density functional theory by machine learning hidden messages from molecules Open
Kohn–Sham density functional theory (DFT) is the basis of modern computational approaches to electronic structures. Their accuracy heavily relies on the exchange-correlation energy functional, which encapsulates electron–electron interacti…
View article: Spintronic superconductor in a bulk layered material with natural spin-valve structure
Spintronic superconductor in a bulk layered material with natural spin-valve structure Open
Multi-layered materials provide fascinating platforms to realize various functional properties, possibly leading to future electronic devices controlled by external fields. In particular, layered magnets coupled with conducting layers have…
View article: Completing density functional theory by machine-learning hidden messages from molecules
Completing density functional theory by machine-learning hidden messages from molecules Open
Kohn-Sham density functional theory is the base of modern computational approaches to electronic structures. Their accuracy vitally relies on the exchange-correlation energy functional, which encapsulates electron-electron interaction beyo…
View article: Coulomb Energy Density Functionals for Nuclear Systems: Recent Studies of Coulomb Exchange and Correlation Functionals
Coulomb Energy Density Functionals for Nuclear Systems: Recent Studies of Coulomb Exchange and Correlation Functionals Open
The Coulomb exchange and correlation energy density functionals for electron systems are applied to nuclearsystems. It is found that the exchange functionals in the generalized gradient approximation provide agreements with the exact-Fock …
View article: Superconductivity of $LaH_{10}$ and $LaH_{16}$: new twist of the story
Superconductivity of $LaH_{10}$ and $LaH_{16}$: new twist of the story Open
We explore high-pressure phase stability and superconductivity of lanthanum hydrides $LaH_m$ (m=4-11,16). We predict stability of a hitherto unreported polyhydride $P6/mmm$-$LaH_{16}$ at pressures above 150 GPa; at 200 GPa its predicted su…
View article: Crystal structure prediction supported by incomplete experimental data
Crystal structure prediction supported by incomplete experimental data Open
The prediction of material structure from chemical composition has been a long-standing challenge in natural science. Although there have been various methodological developments and successes with computer simulations, the prediction of c…