## KIYOKAWA ShujiFaculty Division of Natural Sciences Research Group of Physics Professor |

Last Updated :2021/06/02

- Strongly coupled plasma, atomic processes,ddensity functional theory,Monte Carlo,OCP

Energy barrier of bcc-fcc phase transition via the Bain path in Yukawa system

In the Yukawa system with the dimensionless screening parameter κ> 1.5, when bcc-fcc transition occurs via Bain path, we show that spontaneous transitions do not occur even if the system temperature reaches the transition point of bcc-fcc because it is necessary to increase once the free energy in the process of transition from bcc to fcc through Bain deformation. Here, we refer the temporary increment of the free energy during Bain deformation as Bain barrier. Since there are the Bain barriers at the transitions between bcc and fcc phases, these phases may coexist as metastable state in the wide region (not a coexistence line) of κ and the coupling constant Γ. We study the excess energy of the system and the free energy difference between bcc and fcc phases by the Monte Carlo method, where the simulation box is divided into a large number of elements with small volume and a particle in the box is restricted be placed in one of these elements. By this method, we can tabulate the values of the interparticle potential and can calculate the internal energy fast and precisely., American Institute of Physics Inc., 01 May 2018, Physics of Plasmas, 25 (5), 053703, doiScientific journal

The average ion charge in the thermal ionization

May 2017, High Energy Density Physics, 23, 228-231Supervised Learning of Two-Layer Perceptron under the Existence of External Noise --Learing Curve of Boolean Functions of Two Variables int Tree-Like Architecture--

Aug. 2016, Journal of the Physical Society of Japan, 85 (6), 064001Exact solution to the Coulomb wave using the linearized phase-amplitude method

The author shows that the amplitude equation from the phase-amplitude method of calculating continuum wave functions can be linearized into a 3rd-order differential equation. Using this linearized equation, in the case of the Coulomb potential, the author also shows that the amplitude function has an analytically exact solution represented by means of an irregular confluent hypergeometric function. Furthermore, it is shown that the exact solution for the Coulomb potential reproduces the wave function for free space expressed by the spherical Bessel function. The amplitude equation for the large component of the Dirac spinor is also shown to be the linearized 3rd-order differential equation. (C) 2015 Author(s)., AMER INST PHYSICS, Aug. 2015, AIP ADVANCES, 5 (8), 087150, doi;web_of_scienceScientific journal

Unlearning of Mixed States in the Hopfield Model\n--Finite Loading Case--

Dec. 2014, Journal of the Physical Society of Japan, 84, 014002Multi-average ion model for hot dense plasmas derived from finite temperature density-functional theory

Oct. 2014, High Energy Density Physics, 13, 40A Model of Calculating Radiative Opacities of Hot Dense Plasmas Based on the Density-Functional Theory

Sep. 2014, Journal of Atomic and Molecular Physics, 2014, 431592Learning from Stochastic Rules by Spherical Perceptrons under Finite Temperature -Optimal Temperature and Asymptotic Learning Curve

In the problem of learning under external disturbance, there is a possibility that the existence of some tolerance or flexibility in the system weakens the effect of noise and helps the system to perform more efficiently. In a previous letter, we gave one example of such phenomena in learning from stochastic rules by spherical perceptrons adopting the Gibbs algorithm using statistical mechanical methods. By the replica method, we showed that, in the output noise model, there exists an optimal temperature at which the generalization error takes its minimum for the stable replica symmetric (RS) solution. On the other hand, for other types of noise including input noise, it was shown that no such temperature exists up to the one-step replica symmetry breaking (1RSB) solution. That is, it was shown that for the asymptotic region of a large number of training sets, the RS solution becomes unstable, and the asymptotic behavior is determined by the 1RSB solution, The asymptotic expressions for learning curves were derived, and it turned out that, within the 1RSB solution, the learning curve does not depend on temperature. In this study, we give a detailed derivation of these results and also the results obtained by simulated annealing and exchange Monte Carlo simulation. The numerical results support the theoretical predictions., PHYSICAL SOC JAPAN, Apr. 2011, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 80 (4), 044007, doi;web_of_scienceScientific journal

Derivation of the Fano profile from time-dependent density-functional theory for local thermodynamic equilibrium plasmas

We give the derivation of the Fano profile (the resonance energy position, the resonance width Gamma, and q value) from the time-dependent nonrelativistic density-functional theory (DFT) and propose a scheme for calculating the photoabsorption cross section of hot dense plasmas. As a consequence of this derivation, we show the line profile is obtained as a superposition of Fano and Lorentz profiles when the competition of two optically allowed bound-bound and bound-free transitions occurs. We also show the results of the photoabsorption cross section by applying our scheme to an Fe plasma (density is 7.85 g/cm(3), temperature is 100 eV), where the calculation is carried out without numerical divergence for any photon energy. The calculated results are in good agreement with those of Grimaldi., AMER PHYSICAL SOC, Apr. 2007, PHYSICAL REVIEW A, 75 (4), 042501, doi;web_of_scienceScientific journal

Nucleus-electron model for states changing from a liquid metal to a plasma and the Saha equation

We extend the quantal hypernetted-chain (QHNC) method, which has been proved to yield accurate results for liquid metals, to treat a partially ionized plasma. In a plasma, the electrons change from a quantum to a classical fluid gradually with increasing temperature; the QHNC method applied to the electron gas is in fact able to provide the electron-electron correlation at an arbitrary temperature. As an illustrating example of this approach, we investigate how Liquid rubidium becomes a plasma by increasing the temperature from 0 to 30 eV at a fixed normal ion density 1.03 x 10(22)/cm(3). Th, electron-ion radial distribution function (RDF) in liquid Rb has distinct inner-core and outer-core parts. Even at a temperature of 1 eV, this clear distinction remains as a characteristic of a liquid metal. At a temperature of 3 eV, this distinction disappears, and rubidium becomes a plasma with the ionization 1.21. The temperature variations of bound levels in each ion and the average ionization are calculated in Rb plasmas at the same time. Using the density-functional theory, we also derive the Saha equation applicable even to a high-density plasma at low temperatures. The QHNC method provides a procedure to solve this Saha equation with ease by using a recursive formula; the charge population of differently ionized species are obtained in Rb plasmas at several temperatures. In this way, it is shown that, with the atomic number as the only input, the QHNC method produces the average ionization, the electron-ion and ion-ion RDF's, and the charge population that are consistent with the atomic structure of each ion for a partially ionized plasma. [S1063-651X(99)04809-6]., AMERICAN PHYSICAL SOC, Sep. 1999, PHYSICAL REVIEW E, 60 (3), 3262 - 3272, web_of_scienceScientific journal

One-component plasmas with self-consistently determined core electrons

We present a density functional theory for hot dense plasmas, applicable to high Z atom, where electronic structure of atom as microscopic aspect and ionic distribution as macroscopic aspect are determined self-consistently. In this theory, the plasma is regarded as an ensemble of the virtual 'neutral atom' or, in other words, pseudo neutral atom. We apply our theory to Fe plasmas at temperatures T = 100 eV and 1 keV in the density range 0.1 rho(solid) similar to 200 rho(solid) (rho(solid) = 8.465 x 10(22) cm(-3)), neglecting the polarization of continuum electrons, and consequently obtain the result that the interatomic effective potential is almost the same as the bare-Coulomb type potential in one-component plasmas (OCP). From the obtained profile of the potential upsilon(eff)(r) which determines bound electron states, we suggest a possibility of resonance states. The obtained internal energy for ion subsystem is lower than the Monte Carlo result for OCP, but the difference is within a few percent., PHYSICAL SOC JAPAN, Dec. 1995, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 64 (12), 4708 - 4725, web_of_scienceScientific journal

A FITTING FORMULA FOR SCREENING CONSTANTS OF PARTIALLY-IONIZED ATOMS IN PLASMA

This paper presents a simple fitting formula for the numerical screening constants which were obtained for each of 33 materials recently by the authors [Jpn. J. Appl. Phys. 32 (1993) 5681]. Using the screening constants, the atomic energy levels are obtained for the finite-temperature materials based on the screened-hydrogen model. The formula is convenient for users of the screening constants and reproduces well the Hartree-Fock-Slater (HFS) energy levels: the deviations from the HFS levels are 5.99% for n = 1 and 55.3% for n = 2 by averaging results for the 33 materials. Here n is the principal quantum number., JAPAN J APPLIED PHYSICS, Sep. 1994, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 33 (9A), 5060 - 5061, web_of_scienceIMPROVED SCREENING CONSTANTS FOR PLASMA

We present the new screening constants, with which the atomic energy levels for the finite temperature materials are obtained by the screened-Hydrogen model. The new screening constants axe obtained for each of 33 materials. Each set of screening constants has a temperature dependence in order to realize a better reproducibility of the Hartree-Fock-Slater (HFS) energy levels. The deviations from the HFS calculation are 5.15% for n = 1 and 54.1% for n = 2, based on the average of 33 materials. Here n is the principal quantum number., JAPAN J APPLIED PHYSICS, Dec. 1993, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 32 (12A), 5681 - 5691, web_of_scienceScientific journal

RELATIVISTIC CONFIGURATION-INTERACTION THEORY FOR ATOMIC SYSTEMS

The relativistic configuration-interaction method with analytical relativistic Hartree-Fock-Roothaan (RHFR) basis functions for atomic systems is presented. One-electron functions used for constructing configuration state functions (CSF's) are obtained with the RHFR method in which the large and small components of the radial part of a four-component wave function are expanded in terms of an analytical basis set consisting of Slater-type orbitals. Numerical application of the method to neonlike atomic systems is carried out. It is shown that calculated excitation energies with the method are in good agreement with experiment. The Z-dependent behavior of the optical oscillator strengths for various electric-dipole transitions from the ground state in the systems is also given., AMERICAN PHYSICAL SOC, Dec. 1991, PHYSICAL REVIEW A, 44 (11), 7092 - 7107, web_of_scienceScientific journal

COLLISIONAL-RADIATIVE AND AVERAGE-ION HYBRID MODELS FOR ATOMIC PROCESSES IN HIGH-Z PLASMAS

AMERICAN PHYSICAL SOC, Jan. 1987, PHYSICAL REVIEW A, 35 (1), 233 - 241, web_of_scienceScientific journal

ATOMIC-NUMBER DEPENDENCE OF SOFT-X-RAY EMISSION FROM VARIOUS TARGETS IRRADIATED BY A 0.53-MU-M-WAVELENGTH LASER

AMERICAN PHYSICAL SOC, Jan. 1986, PHYSICAL REVIEW A, 33 (1), 525 - 539, web_of_scienceScientific journal

REDUCED RATE-EQUATION FOR ATOMIC PROCESS IN HIGH-Z PLASMAS

JAPAN J APPLIED PHYSICS, Jan. 1986, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 25 (1), L45 - L47, web_of_scienceScientific journal

THE ANALYSIS OF THE HIGH-RESOLUTION X-RAY-SPECTRA EMITTED FROM A LASER-IRRADIATED GOLD PLASMA

AMER INST PHYSICS, 1985, AIP CONFERENCE PROCEEDINGS, (136), 176 - 185, web_of_science;urlScientific journal

MULTIPLE INNER-SHELL VACANCIES IN LASER-IRRADIATED AU-PLASMA

AMERICAN PHYSICAL SOC, 1985, PHYSICAL REVIEW LETTERS, 54 (18), 1999 - 2002, web_of_scienceScientific journal

ROLE OF LINE AND CONTINUUM OPACITIES IN X-RAY TRANSMISSION THROUGH A LASER-HEATED AU FOIL

JAPAN J APPLIED PHYSICS, 1985, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 24 (6), L439 - L441, web_of_scienceScientific journal

SOFT-X-RAY DRIVEN ABLATION AND ITS POSITIVE USE FOR A NEW EFFICIENT ACCELERATION

JAPAN J APPLIED PHYSICS, 1983, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 22 (2), L88 - L90, web_of_scienceScientific journal

NON-LTE ANALYSIS OF SOFT-X-RAY SPECTRUM FROM LASER-IRRADIATED GOLD PLASMA

JAPAN J APPLIED PHYSICS, 1983, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 22 (12), L772 - L774, web_of_scienceScientific journal