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
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
28
2
1994
Numerical Simulation of Quantum Systems -Dynamics of Electrons in Microstructures-
45
52
EN
Hiroo
Totsuji
Seiji
Hashimoto
Shigetoshi
Nara
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
26
2
1992
Memory Search using Genetic Algorithms and a Neural Network Model
111
128
EN
Shigetoshi
Nara
An information processing task which generates combinatorial explosion and program complexity when it is treated by a serial algorithm is investigated using both Genetic Algorithms (GA) and a neural network model (NN). The task in question is to find a target memory from a set of stored entries in the form of "attractors" in a high dimensional state space. The representation of entries in the memory is distributed ("an auto associative neural network" in this paper), and the problem is to find an attractor under a given access information where the uniqueness or even existence of a solution is not always guaranteed ( an ill-posed problem ). The GA is used as an algorithm for generating a search orbit to search effectively for a state which satisfies the access condition and belongs to the target attractor basin in state space. The NN is used to retrieve the corresponding entry from the network. The results of our computer simulation indicate that the present method is superior to a search method which uses random walk in state space. Our technique may prove useful in the realization of flexible and adaptive information processing, since pattern search in high dimensional state spaces is common in various kinds of parallel information processing.
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
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
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
26
1
1991
Molecular Dynamics ofa Coulomb System with Deformable Periodic Boundary Conditions
51
59
EN
Hiroo
Totsuji
Shigetoshi
Nara
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
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
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
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
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
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
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.