Noriko Watari

Electronic structure of H adsorbed on Pt13 clusters

Electronic structures of Pt13 clusters and those adsorbed with hydrogen atoms based on the first principles calculations are studied for Pt13 clusters of icosahedral (Ih) symmetry, cuboctahedral (Oh) symmetry and the systems of 8,12,14,20 hydrogen atoms adsorbing to them. Calculations have been done by the self-consistent local density functional scheme using the norm-conserving pseudopotential in the linear combination of the atomic orbital method. The equilibrium distances of Pt–Pt and Pt–H are calculated. The electronic structures of H adsorbed on Pt clusters are turned out to be the shell structure of “the giant atom.” H-1s electrons fill n=1 shell of Pt13H cluster with Pt-6s electrons. The energy levels of shell-2d of naked Pt13 clusters and shell-n=3,4 states of H adsorbed Pt13 clusters, which come from H-1s antibonding are compared with experimental results of in situ x-ray absorption near-edge structure (XANES).

First Principles Study of Atomic-Scale Al2O3 Films as Insulators for Magnetic Tunnel Junctions

We performed density-functional calculations with Al/Al2O3/Al structures as models to study Al2O3 tunnel barriers for magnetic tunnel junctions. We found that aluminum oxide films thicker than 4.6 A have pseudogaps without substantial gap states, which suggests that these films have good insulating properties. This finding is consistent with an experimental result where a large magnetoresistance ratio was attained with a film thickness of about 8 A.

CO and NO chemisorption on heavy metal surfaces: cluster model study

Abstract The mechanism for CO or NO strong and weak chemisorptions on tungsten and platinum surfaces is discussed by the cluster model for metal surfaces on the basis of the local density functional scheme using the norm-conserving pseudo-potential in the linear combination of atomic orbitals method. Total energies, stretching frequencies and electronic structures of adsorbed CO and NO molecules obtained by the self-consistent calculations provide us with information to understand the experimental phenomena quantitatively.

Optical Design that Increases Light-Extraction Efficiencies of Organic Light-Emitting Devices through Finite-Difference-Time-Domain Method

The efficiency of light extraction in organic light-emitting devices is insufficient for practical use. This low efficiency is mainly attributed to the refractive index of the light-emitting layer. As the source of an organic light-emitting device is the sum of the point sources, and the wavelength of the emitted light and the scale of the optical structure are comparable, the near-field from the source plays an important role in determining the efficiency with which light is extracted in organic light-emitting devices. Finite-difference time-domain (FDTD) calculations were used to simulate conditions that could not be illustrated with ray optics. We found that the spherical Poynting vector of a point source becomes normal to the high index-ratio interface situated in the near field of the source, and this transformation of the Poynting vector results in the light-extraction efficiency being increased.

Investigation of Disk Bender Low-Frequency Projector with Dual Radiation Surfaces

A low-frequency disk bender projector with dual radiation surfaces was designed on the basis of finite element method (FEM) analysis and equivalent circuit analysis, in order to devise a miniature light weight projector with a high sound pressure level. These analyses suggest that a low-frequency, high-power, miniature and light weight projector can be realized. A trial projector was produced and evaluated. The resonant frequencies for the projector in air and water were 1315 Hz and 970 Hz, respectively. Experimental maximum transmitting voltage sensitivity was 132.2 dB re 1 µPa/V at 1 m.

Total Energy Estimation for Pd/Al Bimetallic Surfaces by a Parallel Computation Scheme

A numerical calculation scheme for the multicenter problem in large molecules and clusters is presented by applying the message-passing interface (MPI) in a massively parallel computer that uses the density functional method. The multicenter problem associated with the Coulomb singularity of an atom is efficiently treated by the parallel processors by allocating several atoms into each processor element (PE). The order N2/P tuning is obtained for the Coulomb energy calculation by using the MPI which transfers Coulomb potential field between PEs. This method is applied to estimate the total energy of the reconstructed Al/Pd bimetallic surface. The energy estimation by the charge density of a superposition of isolated atomic charge fragments predict a stabilization caused by the reconstruction, being consistent with a self-consistent-field (SCF) cluster calculation of the bimetallic surface.

EFFECTIVE POTENTIAL METHOD FOR ELECTRONIC STRUCTURE CALCULATIONS IN MATERIALS DESIGN

A method for electronic structure calculations applicable for any system by new model potentials is presented. The non-local model potentials determined by the first primecples calculation using the norm-conserving pseudopotential are applied for systems of the Si(100) surface dimer and the Pt tip of scanning tunneling microscopy.