arXiv subjects

Tomoya Ono

Publications and source records attributed to Tomoya Ono.

49 records · Page 3Linked to original sources

arXiv2005

First-principles study on scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces

Scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces are studied using first-principles calculations. Our results show that the calculated filled-state images and local density of states are consistent with recent experimental results, and the empty-state images appear significantly different from the filled-state ones. To elucidate the origin of this difference, we examined in detail the local density of states, which affects the images, and found that the bonding and antibonding states of surface silicon atoms largely affect the difference between the filled- and empty-state images.

cond-mat.mtrl-sci↗

arXiv2004

Real-space electronic-structure calculations with timesaving double-grid technique

We present a set of efficient techniques in first-principles electronic-structure calculations utilizing the real-space finite-difference method. These techniques greatly reduce the overhead for performing integrals that involve norm-conserving pseudopotentials, solving Poisson equations, and treating models which have specific periodicities, while keeping a high degree of accuracy. Since real-space methods are inherently local, they have a lot of advantages in applicability and flexibility compared with the conventional plane-wave approach, and promise to be well suited for large and accurate {\it ab initio} calculations. In order to demonstrate the potential power of these techniques, we present several applications for electronic structure calculations of atoms, molecules and a helical nanotube.

cond-mat.mtrl-sci↗

arXiv2004

First-principles study on dielectric properties of NaCl crystal and ultrathin NaCl films under finite external electric field

We present a first-principles study on the dielectric properties of an NaCl crystal and ultrathin NaCl films under a finite external electric field. Our results show that the high-frequency dielectric constant of the films is not affected by the finite size effect from crystal surfaces and is close to that of the crystal, whereas the static one is sensitive to the thickness of the film due to the difference in the atomic configurations between the surface and inside of the film.

cond-mat.mtrl-sci↗

arXiv2004

First-principles study on field evaporation of surface atoms from W(011) and Mo(011) surfaces

The simulations of field-evaporation processes for surface atoms on W(011) and Mo(011) surfaces are implemented using first-principles calculations based on the real-space finite-difference method. The threshold values of the external electric field for evaporation of the surface atoms, which are $\sim$ 6 V/Å2mm for tungsten and $\sim$ 5 V/Å2mm for molybdenum, are in agreement with the experimental results. Whereas field evaporation has been believed to occur as a result of significant local-field enhancement around the evaporating atoms, in this study, the enhancement is not observed around the atoms but above them and the strength of the local field is much smaller than that expected on the basis of the classical model.

cond-mat.mtrl-sci↗

arXiv2004

First-Principles Study on Electron-Conduction Properties of Helical Gold Nanowires

Multishell helical gold nanowires (HGNs) suspended between semi-infinite electrodes are found to exhibit peculiar electron-conduction properties by first-principles calculations based on the density functional theory. Our results that the numbers of conduction channels in the HGNs and their conductances are smaller than those expected from a single-atom-row nanowire verify the recent experiment. In addition, we obtained a more striking result that in the cases of thin HGNs, distinct magnetic fields are induced by the electron current helically flowing around the shells. This finding indicates that the HGNs can be good candidates for nanometer-scale solenoids.

cond-mat.mtrl-sci↗

arXiv2003

First-principles study of electron transport through $C_{20}$ cages

Electron transport properties of C$_{20}$ molecules suspended between gold electrodes are investigated using first-principles calculations. Our study reveals that the conductances are quite sensitive to the number of C$_{20}$ molecules between electrodes: the conductances of C$_{20}$ monomers are near 1 G$_{0}$, while those of dimers are markedly smaller, since incident electrons easily pass the C$_{20}$ molecules and are predominantly scattered at the C$_{20}$-C$_{20}$ junctions. Moreover, we find both channel currents locally circulating the outermost carbon atoms.

cond-mat↗

arXiv2003

First-principles study on field evaporation for silicon atom on Si(001) surface

The simulations of field-evaporation processes for silicon atoms on various Si(001) surfaces are implemented using the first-principles calculations based on the real-space finite-difference method. We find that the atoms which locate on atomically flat Si(001) surfaces and at step edges are easily removed by applying external electric field, and the threshold value of the external electric field for evaporation of atoms on atomically flat Si(001) surfaces, which is predicted between 3.0 and 3.5 V/Å, is in agreement with the experimental data of 3.8 V/Å. In this situation, the local field around an evaporating atom does not play a crucial role. This result is instead interpreted in terms of the bond strength between an evaporating atom and surface.

cond-mat↗

arXiv2003

Geometry and Conductance of Al Wires Suspended between Semi-Infinite Crystalline Electrodes

We present a first-principles study of a coherent relationship between the optimized geometry and conductance of a three-aluminum-atom wire during its elongation process. Our simulation employs the most definite model including semi-infinite crystalline electrodes using the overbridging boundary-matching method [Phys. Rev. B {\bf 67}, 195315 (2003)] extended to incorporate nonlocal pseudopotentials. The results that the conductance of the wire is $\sim$ 1 G$_0$ and the conductance trace as a function of electrode spacing shows a convex downward curve before breaking are in agreement with experimental data.

cond-mat↗

arXiv2003

Magnetic orderings in Al nanowires suspended between electrodes

A theoretical analysis of a relation between atomic and spin-electronic structures for the ground state of single-row aluminum nanowires suspended between Al(001) electrodes is demonstrated using first-principles molecular-dynamics simulations. We obtain a unusual result that a 3-aluminum-atom nanowire sandwiched between the electrodes does not manifest magnetic ordering although an isolated aluminum trimer molecule in a straight line is spin-polarized. On the other hand, a 5-atom nanowire exhibits ferromagnetic ordering, where three central atoms form a spin-polarized trimer. Moreover, in the case of an 8-atom nanowire, the middle atoms in the nanowire form two spin-polarized trimers with antiferromagnetic ordering.

cond-mat↗

arXiv2002

First-Principles Study on Peierls Instability in Infinite Single-Row Al Wires

We present the relation between the atomic and spin-electronic structures of infinite single-row atomic wires made of Al atoms during their elongation using first-principles molecular-dynamics simulations. Our study reveals that the Peierls transition indeed occurs in the wire with magnetic ordering: it ruptures to form a trimerized structure with antiferromagnetic ordering and changes from a conductor to an insulator just before forming a linear wire of equally-spaced atoms. The formation of the trimerized wire is discussed in terms of the behavior of the $σ$-symmetry bands of the Al wire.

cond-mat↗

arXiv2002

Coherent Relation between Structure and Conduction of Infinite Atomic Wires

We demonstrate a theoretical analysis concerning the geometrical structures and electrical conduction of infinite monatomic gold and aluminum wires in the process of their elongation, based on first-principles molecular-dynamics simulations using the real-space finite-difference method. Our study predicts that the single-row gold wire ruptures up to form a dimer coupling structure when the average interatomic distance increases up to more than 3.0 A, and that the wire is conductive before breaking but changes to an insulator at the rupturing point. In the case of the alumi-num wire, it exhibits a magnetic ordering due to the spin polarization, and even when stretched up to the average interatomic distance of 3.5 A, a dimerization does not oc-cur and the wire keeps a metallic nature.

cond-mat↗

arXiv2000

Direct Minimization Generating Electronic States with Proper Occupation Numbers

We carry out the direct minimization of the energy functional proposed by Mauri, Galli and Car to derive the correct self-consistent ground state with fractional occupation numbers for a system degenerating at the Fermi level. As a consequence, this approach enables us to determine the electronic structure of metallic systems to a high degree of accuracy without the aid of level broadening of the Fermi-distribution function. The efficiency of the method is illustrated by calculating the ground-state energy of C$_2$ and Si$_2$ molecules and the W(110) surface to which a tungsten adatom is adsorbed.

cond-mat↗

arXiv1999

Timesaving Double-Grid Method for Real-Space Electronic-Structure Calculations

We present a simple and efficient technique in ab initio electronic-structure calculation utilizing real-space double-grid with a high density of grid points in the vicinity of nuclei. This technique promises to greatly reduce the overhead for performing the integrals that involves non-local parts of pseudopotentials, with keeping a high degree of accuracy. Our procedure gives rise to no Pulay forces, unlike other real-space methods using adaptive coordinates. Moreover, we demonstrate the potential power of the method by calculating several properties of atoms and molecules.

cond-mat↗