Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
29
1
1994
Electronic States in Semiconductor Quantum Dot with Fluctuating Interfaces
7
14
EN
Hiroo
Totsuji
Shigetoshi
Nara
Chieko
Totsuji
10.18926/20011
Effects of interface fluctuations on the electronic states in semiconductor quantum dots are analyzed on the basis of numerical solutions for ground state wave functions and
energy eigenvalues. It is shown that the effective volume of confinement becomes smaller than the real volume of quantum dots due to fluctuation. This effect comes from the
fact that the wave functions with larger characteristic wavelength are not able to deform themselves following the fluctuation of interfaces exactly.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
33
2
1999
O(N) Tight-Binding Algorithm for Large-Scale Molecular Dynamics Simulations
71
77
EN
Kenji
Tsuruta
Hiroo
Totsuji
Chieko
Totsuji
10.18926/19674
A parallel tight-binding molecular dynamics with an order-N [O(N))] algorithm is implemented to perform large-scale simulation of nanostructured materials. The algorithm is based on the Fermi-operator expansion of an electronic energy and force, and we present its basic formalisms. Accuracy necessary for molecular-dynamics simulations can be obtained by a proper truncation in the expansion. Parallel efficiency on a parallel PC cluster shows nearly ideal scaling behavior with respect to the number of processors. Applicability of the method to a silicon-carbide system is examined.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
33
2
1999
Multicomponent Plasmas in Penning-Malmberg Traps
61
69
EN
Hiroo
Totsuji
Kenji
Tsuruta
Chieko
Totsuji
10.18926/19673
The behavior of multicomponent plasmas in the Penning-Malmberg traps is discussed with the parameters corresponding to experiments with antiprotons and cryogenic electrons. The relaxation times for the energy transfer antiprotons to electrons and between parallel and perpendicular components of electrons are estimated. It is shown that, depending on the values of parameters, both the former and the latter can be the bottleneck in the cooling process.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
33
2
1999
Density Functional Molecular Dynamics of Hydrogen Plasma
51
59
EN
Hiroo
Totsuji
Kenji
Tsuruta
Chieko
Totsuji
10.18926/19671
Density functional molecular dynamics method is applied to hydrogen plasma in the domain of liquid metallic hydrogen. Tentative results for the proton-proton pair distribution function and the electron-proton pair distribution function are obtained. It is shown that with the increase of the parameter ƒÁ(s), we have increasingly strong screening of proton charge by electrons and the decrease of electron density in the domain between protons.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
32
1-2
1998
Structure of Yukawa (Dusty Plasma) Mixtures
23
41
EN
Hiroo
Totsuji
Tokunari
Kishimoto
Chieko
Totsuji
10.18926/19636
Parameters characterizing the structure ot confined Yukawa system are estimated for 'dusty plasmas', clouds of charged macroscopic particles formed near the boundary between plasma and the sheath and leviated by negatively biased electrode. When we have dust particles with different ratios of charge to mass, they form a two-dimensional Yukawa mixture or separate two-dimensional one-companent Yukawa systems, depending on the charge density in the sheath and number density of dust particles. In order to provide a basis for numerical simulations on Yukawa mixtures including Coulombic case, we summarize mathematical expressions necessary for molecular dynamics.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
1349-6115
43
2009
Experimental Conditions for Observation of ThermodynamicInstability and Critical Point of Fine Particle (Dusty) Plasmas
27
31
EN
Hiroo
Totsuji
10.18926/17833
When the Coulomb coupling between fine particles becomes sufficiently strong in fine particle plasmas, the isothermal compressibility of the whole system diverges and we have a phase separation and an associated critical point. Experimental conditions of fine particle plasmas, densities and temperatures of components and the fine particle size, are obtained corresponding to characteristic parameters around the critical point and the dependency on ion species and other factors is discussed.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
1349-6115
43
2009
Information Transfer and Entanglement Creation by Spin Chains: Effects of Noise and Asymmetry
22
26
EN
Hiroo
Totsuji
Chieko
Totsuji
Kenji
Tsuruta
10.18926/17831
For the transfer of quantum information and the creation of entangled states, the application of tuned spin chains, systems of spins with the nearest-neighbor coupling tuned so as to give high efficiency, has been proposed and some examples of high performance have been given by several authors. In this article, the effect of deviations from tuned values and the effect of resultant asymmetry are investigated through numerical simulations and theoretical analyses. It is shown that there exists a system where the transfer efficiency is comparable with exactly tuned ones and, at the same time, robust to noises in the coupling constants. It is also shown that the effect of asymmetry on the efficiency of entanglement creation is of the second order when the asymmetry is small.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
1349-6115
43
2009
FDTD Simulations of Acoustic Waves in Two-DimensionalPhononic Crystals using Parallel Computer
16
21
EN
Kenji
Tsuruta
Chieko
Totsuji
Hiroo
Totsuji
10.18926/17829
The finite-difference time-domain (FDTD) method has been applied to the calculation of the phonon band structure of two-dimensional (2D) phononic crystals, consisting of metal cylinders placed periodically in liquid. By comparing several combinations of materials for metal cylinder and liquid, we analyze the dependence of the band structures on sound speed and density of liquid media. Moreover, the negative refraction of the acoustic waves is observed at the interfaces between phononic crystal slab and the liquid. We find that an acousticglens effecthwith the slab appears due to the negative refractions. The relationship between the focal intensity in the lens effect and the band structure is discussed.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
1349-6115
43
2009
Dispersion Models and Electromagnetic FDTD Analyses ofNanostructured Metamaterials using Parallel Computer
8
15
EN
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/17826
Metamaterial which has negative permittivity and permeability is investigated via computer simulations. Effects of the nanostructure on dielectric and magnetic properties of the material are taken into account by introducing the Drude-Lorentz model in the materials dispersion. We include multi-band process in the dielectric response in order to reproduce accurately experimental values of bulk Au thin film. Size effect on the dispersion is examined by comparing the model with that of a noble metal particle. Based on the dispersion model constructed, we analyze the electromagnetic response of nanostructured metamaterials to evanescent waves at microwave and optical frequencies via finite-difference time-domain simulatioins on parallel computer. A re- focusing and an amplification of the evanescent waves propagating through a metamaterial, consisting of metal
slab/vacuum stacking, is demonstrated for the frequencies of 30GHz and 744THz.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
24
2
1990
Control of Microscopic Superconducting Channel by the Proximity Effect
41
47
EN
Hiroo
Totsuji
10.18926/15497
A possibility to control the microscopic superconducting
channel based on the proximity effect is theoretically shown by a simple one-dimensional analysis of de Gennes' equation for the order parameter.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
25
1
1990
Superconductivity Proximity Effect in Inhomogeneous Media
51
57
EN
Hiroo
Totsuji
10.18926/15490
The superconductivity proximity effect in the dirty limit is revisited and equations and boundary conditions are obtained for the case of inhomogeneous media with continuously varying characteristic parameters.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
24
1
1989
Propagation Characteristics of Superlattice Potentials and their Optimization
93
105
EN
Hiroo
Totsuji
Teruki
Hatatani
10.18926/15482
Propagation of charged carriers in semiconductor
superlattices is analyzed on the basis of the effective mass approximation with appropriate boundary conditions at heterojunctions taken into account. Applying the finite element method, clarified are the effects of details of the potential profile, such as linear and smooth gradings and random fluctuations, on characteristics of superlattices which are expected to work as collector barriers and energy filters in electronic devices.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
23
1
1988
Plasma Oscillation in Semiconductor Superlattice Structure
69
82
EN
Hiroo
Totsuji
10.18926/15468
The statistical properties of two-dimensional systems of charges in semiconductor superlattices are analyzed and the dispersion relation of the plasma oscillation is calculated. The possibility to excite these oscillations by applying the electric field parallel to the structure is discussed.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
28
2
1994
Numerical Simulation of Quantum Systems -Dynamics of Electrons in Microstructures-
45
52
EN
Hiroo
Totsuji
Seiji
Hashimoto
Shigetoshi
Nara
10.18926/15460
Difficulties in simulating systems composed of classical and quantum particles lie in the treatment of the many-body interactions between quantum particles and the geometrical variety of configurations of classical particles. In order to overcome these difficulties, we have developed some numerical methods and applied them to simple cases. As for stationary states, the finite element method provides us with sufficient geometrical freedom.
Combined with the Kohn-Sham equation based on the density
functional theory, this method virtually satisfies our requirement. In order to investigate time-dependent phenomena, we apply the time-dependent Kohn-Sham equation. Adopting the finite difference method, we are able to follow the development of quantum many-body system. As an example, we estimate the effects of the potential height, the electric field, and many-body interactions in some transition processes in quantum wells coupled by a tunneling barrier. This example is important in itself in relation to semiconductor superlattices and also serves as a benchmark for quantum simulations, variety of geometry
corresponding to that of classical particles.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
22
1988
Thermodynamic Sum Rules for Mixtures of Charged Particles
35
44
EN
Hiroo
Totsuji
10.18926/15450
Several methods to derive thermodynamic sum rules for a system including charged particle are proposed and applied to charged mixtures as well as one-component systems. The validity of the statements is examined carefully with respect to the ordering in the powers of the wave number. As for the mixture of electrons and ions, it is shown how the aspect of the one-component plasma or the ionic mixture appears when electrons become strongly degenerate.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
22
1988
One-Electron State of a Partially Ionized High-Z Ion
15
34
EN
Yoichiro
Furutani
Hiroo
Totsuji
10.18926/15449
An effective potential of an isolated partially ionized high-Z ion, calculated within the framework of the statistical models of atoms, is injected into the one-electron Schrödinger equation, in view of evaluating the electron density and comparing it with the results of statistical models. Starting from this initial value, a self-consistent electron density is obtained on the basis of the density functional theory, where quantum natures of electrons are fully taken into account.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
26
2
1992
Spectrum of Schottky Noise in Ion Storage Rings
129
138
EN
Hiroo
Totsuji
10.18926/15444
The spectrum of Schottky noise in ion storage rings is analyzed as density fluctuations in effectively one-dimensional plasmas. Strong coupling effects in these plasmas are discussed in relation to experimental observations.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
28
1
1993
Ground State of Coupled Quantum Wires
27
38
EN
Hiroo
Totsuji
Shigetoshi
Nara
10.18926/15434
The ground states of interacting electrons in coupled quantum wires are analyzed on the basis of the density functional theory. The exchange-correlation potential is calculated from 'exact' results given by the Green's function Monte Carlo method in two and three dimensions. It is shown that the critical density signifying the change from symmetrical to asymmetrical ground state is weakly dependent on the details of the exchange-correlation potential. These critical values are compared with the result of the three-dimensional analysis for a single wire.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
28
1
1993
A Simple Method to Evaluate Structural Stability of Group IV and III-V Semiconductors
1
25
EN
Shigetoshi
Nara
Hiroo
Totsuji
10.18926/15432
The structural stabilities of bulk Si, Ge, and GaAs are discussed based on the total energy evaluated by the summation of the band structure energy and the short-range repulsive potential between ions. The band structure energy
is calculated by means of the simple tight-binding method. The tight-binding parameters are determined so as to fit to the results of a pseude potential calculation and Harrison's model is employed to include the influence of lattice deformation. The short-range-force is assumed to be of the exponential form and parameters are determined so as to reproduce an experimental value of bulk modulus. This treatment qualitatively well describes structural properties in spite of the simple computational procedure and roughly gives the known variation of the total energy for a <100> uniaxial strain. This method is able to be applied to an investigation of the structural stabilities of superlattices, for example, a strained layer superlattice consisting of hetero-semiconductors.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
29
2
1995
One-Dimensional Classical Plasmas in Ion Traps, Ion Storage Rings, and Semiconductor Quantum Wires
57
65
EN
Hiroo
Totsuji
10.18926/15422
As plasmas with extremely reduced dimensionality, properties of one-dimensional classical plasmas are analyzed in the domain of strong coupling and static and dynamic structure factors and the plasmon dispersion relation are obtained. These plasmas may be realized in Penning traps with sufficiently strong confinement and also in semiconductor quantum wires under appropriate conditions.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
26
1
1991
Molecular Dynamics ofa Coulomb System with Deformable Periodic Boundary Conditions
51
59
EN
Hiroo
Totsuji
Shigetoshi
Nara
10.18926/15418
Variable shape molecular dynamics is formulated for the one-component plasma and the structural transition from the fcc lattice to the bcc lattice has been observed. It is emphasized that the condition of constant volume should be imposed when deformations of periodic boundary conditions are taken into account.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
27
2
1993
Complex Dynamics and Search in A Cycle-Memory Neural Network
19
40
EN
Shigetoshi
Nara
Hiroo
Totsuji
10.18926/15403
Numerical simulations of a single layer recurrent neural network model in which the synaptic connection matrix is formed by summing cyclic products of succesive patterns show that complex dynamics can occur with the reduction of a connectivity parameter which is the number of connection between neurons. The structure in these dynamics is discussed from the viewpoint of realizing complex function using complex dynamics.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
30
2
1996
Yukawa System in One-Dimensional External Field
27
37
EN
Hiroo
Totsuji
Tokunari
Kishimoto
Chieko
Totsuji
10.18926/15402
The behavior of the Yukawa system in external one-dimensional force fields is analyzed by the molecular dynamics simulation. The formation of layered structures at low temperatures is observed and the relation between the number of layers and characteristic parameters of the system is obtained. Since the Yukawa system serves as a model of clouds of dust particles in plasmas (dusty plasma) which play an important role in plasma processes of semiconductor engineering, the results may be useful to control the quality of semiconductor wafers in such processes. In simulations, periodic boundary conditions are
imposed in two dimensions and deformations of periodic boundaries are allowed in order to reduce the effect of boundaries without giving too much constraint on the symmetry.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
30
2
1996
Analysis of Quantum Waveguide : Effective Width and Height of Potential for Quantum Wires under Split Gates
21
25
EN
Hiroo
Totsuji
10.18926/15401
In order to apply quantum waveguides to electronic devices, we calculate the electrostatic potential in the split-gate quantum wire and establish the relation between the electrostatic potential and the square well potential which is usually assumed in simulations of these waveguides. The height and width of the square well potential are expressed as simple functions of the gate voltage and their dependencies are clarified. The results may be useful in calculating the characteristics of
electronic devices based on quantum waveguides as functions of controllable parameters such as gate voltage.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
27
1
1992
Electronic States and Electron Wave Transfer in Coupled Quantum Wires and Its Control by Externally Applied Electric Field
65
79
EN
Shigetoshi
Nara
Hiroo
Totsuji
10.18926/15395
Quantum mechnical electron wave transfer between two quantum wires which are weakly coupled via a thin potential barrier is considered. The total electronic states are calculated with both analytical ( no field case ) and numerical methods ( under applied electric fields ). The transfer efficiency is evaluated for several specified cases of geometrical structures, potential barrier heights and the externally applied electric field. Estimated trasfer time is of the order of one picosecond in typical mesoscopic structures. The model in this paper can be used to determine important structure parameters for experiments on electron directional coupler controled by external elctric field.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
27
1
1992
Intrinsic Bistability of Coupled Quantum Wires: Localization due to Many-Body Effects
55
64
EN
Hiroo
Totsuji
Shigetoshi
Nara
10.18926/15394
The ground state of a system of electrons accumulated in a pair of coupled symmetric quantum wires is analyzed on the basis of density functional theory. It is shown that, in a domain of physical parameters, electrons are localized in either of wires. The main contribution to the total energy of this system comes from the Hartree energy, or the electrostatic energy, and the exchange-correlation energy between electrons. The ground state is determined by a competition between these contributions: We have symmetric electron distributions when the Hartree energy dominates and asymmetric (localized) states are realized in the opposite case. This kind of simple system with bistable electronic states may be applied to semiconductor memory devices.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
30
1
1995
Electronic Structure of Mixed Perovskite Oxides
89
97
EN
Chieko
Totsuji
Hiroo
Totsuji
10.18926/15383
Based on the tight-binding method, electronic bands of the mixed perovskite oxides are calculated in order to develop the electronic theory of ferroelectric phase transitions in these mixtures which are difficult to describe within the phenomenological theories. Diagonal elements of Hamiltonian matrix of parent materials are assumed to differ by 0.1eV and mixtures are simulated by lattices of supercells containing 2(3) = 8 or 3(3) = 27 unit cells randomly assigned to either material. The width of the conduction and valence bands have maxima and the band gap has a minimum at intermediate mixing ratio. Results are in agreement with those of other analyses on random systems and even 2(3)-cell computation seems to serve as a first approximation for our purpose.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
30
1
1995
Molecular Dynamics of Yukawa System (Dust Plasma) with Deformable Periodic Boundary Conditions: Formulation
75
87
EN
Hiroo
Totsuji
Yoshihiko
Inoue
Tokunari
Kishimoto
Chieko
Totsuji
Shigetoshi
Nara
10.18926/15381
Molecular dynamics of the Yukawa system, the system of particles interacting via the Yukawa or the screened Coulomb potential, are formulated for various statistical ensembles and external conditions. The Yukawa potential smoothly interpolates the long-range Coulomb and the short-range interactions by adjusting a single parameter, the
screening length. In order to reduce the effect of boundaries, the periodic boundary conditions are imposed and the deformations of the fundamental vectors of periodicity are taken into account. Ewald-type expressions for interaction energy, force, and kinematic pressure are
given explicitly.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
35
1-2
2001
Molecular Dynamics of Yukawa System using the Fast Multipole Method
77
95
EN
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/15361
In order to perform the large-scale molecular dynamics simulation of the Yukawa system, a mathematical expression for molecular dynamics using the fast multipole method is described. The model simulations are also performed to test
the performance of our implementation of the FMM.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
35
1-2
2001
Nonorthogonal Tight-Binding Molecular Dynamics for Si(1-x)Ge(x) Alloys
63
75
EN
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/15358
We present a theoretical study of Si(1-x)Ge(x) alloys based on tight-binding molecular dynamics (TBMD) calculations. First, we introduce a new set of nonorthogonal tight-binding parameters for silicon and germanium based on the previous work by Menon and Subbaswamy [Phys. Rev. B 55, 9231 (1997); J. Phys: Condens. Matter 10, 10991 (1998)]. We then apply the method to structural analyses of Si(1-x)Ge(x) alloys. The equilibrium volume and atomic structure for a given x are obtained by the TBMD method. We also calculate the bulk modulus B, elastic constants C(11), C(12) and C(44) as a function of x. The results show that the moduli vary monotonically, but nonlinearly, between the values of Si crystal and Ge crystal. The validity of the results is also discussed.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
31
1
1996
Structure of Dusty Plasma as Yukawa System Confined in One-Dimensional External Fields
19
33
EN
Hiroo
Totsuji
Tokunari
Kishimoto
Chieko
Totsuji
10.18926/15166
As a model of dusty plasmas in external fields, Yuka.wa system in a one-dimensional external field is analyzed by molecular dynamics simulations and theoretical approaches. It is shown that particles form clear thin layers (sheets) at low temperatures and the number of layers changes discretely with characteristic parameters of the system, accompanying the rearrangements of whole system from nearly equipartitioned layers to also nearly equipartitioned layers. The number, positions and populations of layers are obtained as functions of characteristic parameters. The shell (sheet) model which has been successful for confined one-component plasmas is extended to this system and results of numerical experiments are reproduced to a good accuracy. The effect of cohesive energy in each layer is of essential importance to reproduce discrete changes in the number of sheets.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
39
1
2005
Large-Scale Molecular Dynamics Simulation of CoulombClusters: A Finite-Temperature Analysis
52
55
EN
Katsuya
Kanamori
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14152
Thermal behavior of Coulomb clusters in a three dimensional confining potential is investigated by molecular dynamics simulations for system sizes of 1,000 to 20,288 ions. The specific heat of the system of shell-structured 20,000 ions is peaked almost at the same temperature as the system of
bcc-structured 20,288 ions with much sharper structure for the latter. The diffusion coefficient and the peak to valley ratio of the two-dimensional pair distribution function on the outermost shell are obtained both as a function of temperature. The rotational movement of each shell in the system
of 104 ions is observed.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
39
1
2005
Electron Dynamics in Semiconducting Nanowires: A Real-Space,Polynomial-Expansion Approach
46
51
EN
Keisuke
Kadono
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14150
We present a real-space, polynomial-expansion approach to electron dynamics in nanostructured semiconductors. The Chebyshev expansion method is employed for efficient calculation of timeevolution of single-electron wave function. Details of the formulation are described. The method is applied to the electron transport in nanostructured semiconductors such as Si nanowires. The
mean-square displacement and diffusivity of electron in Si chains are obtained as functions of length of the chains. The results show clearly ballistic behavior of electron in the pure Si chain.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
40
1
2006
Distribution of Electrons in Quantum Dots Analyzed by Classical Mapping and Molecular Dynamics
40
43
EN
Miyake
Takashi
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14121
The electron system of arbitrary degeneracy can be mapped onto a classical system where electrons of the same spin are assigned an additional interaction and the effect of degeneracy is taken into account through an imaginative temperature. We apply this method to electrons in quantum dots modeled as two-dimensional electron liquid confined in a finite domain by a harmonic potential. We analyze distribution functions by molecular dynamics instead of solving integral equations which are not so useful in the case without translational invariance.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
40
1
2006
Stochastic-Dierence-Equation Method for Long Time-scaleMolecular Dynamics Simulations
36
39
EN
Atsushi
Uchida
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14120
We present a Stochastic-Difference-Equation (SDE) approach to long time-scale molecular dynamics (MD) simulations, which are required for nanosecond-scale phenomena. In this method, the MD trajectory in a fixed time period is obtained as a stationary solution of an action functional
based on an error accumulation of the equation of motion along the path, thus reducing the problem to a boundary-value problem, instead of an initial-value problem in the ordinary MD method. We apply the method to formation processes of Cu thin film via nanocluster deposition onto a substrate.
The applicability of the SDE algorithm to the problem and the effects of the choice of SDE parameters on the optimization processes of configuration pathway are examined.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
40
1
2006
Melting of Spherical Yukawa Clusters Analyzed by Monte CarloSimulation
31
35
EN
Takafumi
Ogawa
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14119
We analyze the melting of spherical Yukawa clusters by Monte Carlo simulations. Spherical clusters are expected to be found in dusty plasmas in an isotropic environment such as microgravity and serve as a model for classical clusters. We obtain the specific heat through fluctuations of the potential energy and identify its peak as the transition temperature. Melting temperatures are compared with those of bulk Yukawa systems and it is confirmed that the melting temperature increases and approaches the bulk value with the increase of the system size.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
42
1
2008
Spin Polarization of Two-Dimensional Electron System in a Finite Domain
56
59
EN
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14061
We analyze the ground state of the two-dimensional quantum system of electrons confined in a parabolic potential with the system size around 100. We map the system onto a classical system on the basis of the classical-map hypernetted-chain (CHNC) method which has been proven to work in the integral-equation-based analyses of uniform unbounded systems and then apply classical numerical simulations. We find that the confined system undergoes the transition to the spin polarized state with the decrease of the average density and the corresponding critical value is as low as rs ∼ 0.3 in terms of the usual rs parameter estimated for the average density. As the ground state
for given value of the rs parameter, our data give the critical value for the transition around 20 which
is consistent with the known possibility. The advantage of our method is a direct applicability to geometrically complex systems which are difficult to analyze by integral equations. The application to the structure like quantum dots reported here is the first example of such applications.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
42
1
2008
Transfer of Quantum Information by Spin Chains : Effect of Noise
53
55
EN
Hiroo
Totsuji
10.18926/14060
In order to transfer quantum information, the use of spin chains has been proposed and their transfer characteristics have been analyzed. As one of the latter, the maximum of the transfer probability over sufficiently long time period is often considered important and some examples with high maximum values have been given. In these examples, the coupling between neighboring spins are tuned so as to attain high efficiency. In this article, we discuss the effect of noise on the values of coupling constant. As a result, we propose a system where the efficiency is high and also the effect of noise is small.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
42
1
2008
Numerical Simulations of Two-dimensional Electron Fluid : An Application of Classical-map Hypernetted-chain Method
48
52
EN
Chieko
Totsuji
Kenji
Tsuruta
Hiroo
Totsuji
10.18926/14059
Based on the mapping introduced by the classical-map hypernetted-chain (CHNC) method, classical
numerical simulations, Monte Carlo and molecular dynamics, have been applied to the twodimensional
electron fluid and the results are compared with those of quantum Monte Carlo simulations
hitherto reported. It is shown that polarization properties of the ground state obtained by the diffusion Monte Carlo method are reproduced within the accuracy of quantum simulations by both of two mapping functions for the quantum temperature which have been proposed within the
CHNC method. These results may serve as the basis of numerical simulations based on the CHNC method which are applicable to finite non-periodic systems like quantum dots and systems at finite temperatures.
No potential conflict of interest relevant to this article was reported.
Faculty of Engineering, Okayama University
Acta Medica Okayama
0475-0071
42
1
2008
Vibrational Properties of Si Crystal with Vacancy : A Tight-Binding Study
44
47
EN
Kenji
Tsuruta
Chieko
Totsuji
Hiroo
Totsuji
10.18926/14058
To analyze vibrational properties of Si crystal with a single charge-neutral vacancy, we perform large-scale simulations based on tight-binding molecular-dynamics method.
Vibrational modes and frequencies are obtained by diagonalizing dynamical matrix within a harmonic approximation. Results indicate that there exist vibrational modes spatially localized around the vacancy and large frequency shifts associated with the localized
modes contribute significantly to reduction of the vibrational free energy.
No potential conflict of interest relevant to this article was reported.