Kazume Nishidate

First principles calculations for electronic band structure of single-walled carbon nanotube under uniaxial strain

Electronic band structures of single-walled carbon nanotubes (SWNTs) are studied using first principles ultrasoft pseudopotential with plane wave basis. We find that band gap values of relaxed SWNTs in the generalized gradient approximation significantly differ from those obtained in the local density approximation for the exchange-correlation functional. In addition, it is shown that electronic band structures and total energies of SWNTs are strongly correlated with axial strain.

ASECA: a cellular-automata simulation program for a silicon anisotropic super-micro-etching process in aqueous KOH

A three-dimensional anisotropic super micro-etching of crystalline silicon in aqueous KOH is simulated on an atomic level using a new three-dimensional cellular-automata calculational method. The etching simulator ASECA is developed using a rule-based functional Mathematica programming style. The complete program codes and a detailed description of the algorithm are presented.

Pressure-Controlled Tight-Binding Molecular Dynamics Simulation of Carbon Nanotubes

Properties of (10, 10) single-walled carbon nanotubes under uniaxial pressure are investigated by means of pressure-controlled molecular dynamics simulations using an order- N tight-binding method. We use an extended Andersen method in order to control pressure of system. This scheme allows us to investigate the pressure-dependence of structural stability as a function of time in the presence of many-body quantum mechanical effect. At small strains, the potential energy of the carbon nanotube increases in accordance with the Hookes law. In this elastic regime, the carbon nanotube keeps straight as a whole. The finite temperature effects on the strains are analyzed.

Molecular dynamics study of a V2O5 crystal

Abstract V 2 O 5 crystal has been simulated by means of molecular dynamics calculational method. A new simple interatomic potential model for the crystal was developed so that the crystal structure remains quite stable for all the simulation time steps. The averaged distribution of O–V–O bond angles in the simulation was compared with the experimental data. Finally, the model was applied to simulate the diffusion dynamics of oxygen atoms in the crystal.

Improved Organic Thin Film Transistor Performance Utilizing a DH-α6T Submonolayer

In this paper, we have reported on improved titanyl phthalocyanine (TiOPc) thin film transistor (TFT) performance utilizing an α,α′-dihexylsexithiophene (DH-α6T) submonolayer. By the detailed XRD and AFM analysis, highly ordering α-TiOPc thin films could be deposited on SiO2/Si substrates modified by a DH-α6T submonolayer. Organic TFT with a TiOPc/ DH-α6T bilayer as active layers realized high mobility of 2.45 × 10−1 cm2 /V s, which is about 100 times greater than that of TiOPc single layer device.

Formation of an S2- Molecular Ion and Its Luminescence Characteristics in KCl:MnS Crystals

It was found that when a KCl crystal doubly doped with a trace of MnS was irradiated with UV light, the S2- molecular ions were effectively produced through a photochemical reaction. These S2- molecular ions exhibited characteristic vibronic luminescence composed of zero-phonon lines and phonon-side bands below 160 K. Such a vibronic structure related to zero-phonon lines could also be observed for the first time in the luminescence excitation band. From the analysis of the spectral positions of zero-phonon lines in the emission and excitation spectra, the average vibrational frequencies of the S2- molecular ion in the ground state and excited state were determined to be 1.78×1013 s-1 and 1.13×1013 s-1 respectively.

A Toolkit for Programming Cellular Automata

The structure of a CA is extremely simple when written in the Mathematica programming language: a matrix is set up, a function (CA rule) is defined, and the function is repeatedly applied to the matrix. In this chapter we will lay the foundations for the CA programming in the chapters that follow. We first give both a physical and a computational definition of a cellular automaton. Then we discuss the operation of code fragments that repeatedly appear in CA programs throughout the book. Reading the programs in the book with an understanding of how these code fragments work will allow you to focus on the principal programming task in writing a CA program in Mathematica—defining the CA rules.

Cellular Automaton Model for Biased Diffusive Traffic Flow

A new stochastic discrete space-time model is proposed to simulate a biased diffusive system of two species in two dimensions. A very simple rule set which prohibits the multiple occupancy of a lattice sites by particles while conserving their number, is used to define the dynamics. We found that spatial inhomogeneous bands in high-density states promptly form as the time step increases. The biased diffusive cell automaton ( BDCA ) model is analyzed and discussed.

Tuning the work function of graphene with the adsorbed organic molecules: first-principles calculations

ABSTRACT We have investigated the energetics and work function (WF) of graphene (GR) with depositing pentacene (C22H14, PEN) and perfluorinated pentacene (C22F14, PFP) using the electronic structure calculations based on the density functional theory with van der Waals (vdW) corrections. Both molecules are adsorbed on GR in flat-laying form with the height of 3.2 Å through vdW interaction, and no explicit exchange of electrons was found between GR and adsorbed molecules. However, we found charge redistribution in the surface to interface region and this brings about the vacuum level shifts, Δ = −0.06 eV for PEN and Δ = +0.10 eV for PFP, demonstrating that the work function of GR can be tuned by the physisorption of organic molecules.

Vibronic Structures in Excitation and Emission Spectra Characteristics of O2- Molecular Ions in KI, KBr and KCl Crystals

The excitation and emission spectra of O2- molecular ions in KI, KBr and KCl crystals have systematically been investigated at 8.7 K. The present results for the emission spectra with zero-phonon lines were in good agreement with previous results. From the temperature dependence of their emissions, we found that the luminescence intensities of O2- ions still appear at room temperature (RT) and are much stronger than those of other chalcogen molecular ions particularly in a KCl crystal. On the other hand, we found vibronic structures on the low-energy sides of the excitation spectra of KI and KBr:O2- crystals, showing several peaks with nearly equidistant spacings. The anharmonic vibrational energies of O2- molecular ions in the excited state were obtained from these energy differences, depending on their lattice constants. Using spectroscopic constants calculated from the experimental data, we could construct a configurational-coordinate diagram for an O2- center in a KI:O2- crystal.