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BaTiO3 is a well-known piezoelectric material with commercial uses. The ferroelectric state of BaTiO3 generally comprises electrically polarized domains separated by domain walls (DWs). The DW alters local polarization vectors by an angle of 90° for 90° DW or 180° for 180° DW. The DW is crucial to piezoelectric properties such as response time and fatigue. Furthermore, the DW structure and its dynamics in BaTiO3 are not well understood. Hence, for the first time, we theoretically obtained the atomistic structure of the 90° DW via molecular dynamics simulations at 300 K with the core–shell interatomic potential, using a large-scale system with a side length of 2.8 × 10 3 Å. The width of the 90° DW thereby obtained was approximately 30 Å, which was 20 Å wider than that of the 180° DW. Under the external electric field E → ext parallel to the DW, we observed an extension of a domain having a polarization vector with a positive component along the E → ext-direction. The migration velocity of the 90° DW was approximately two times that of the 180° DW at the same E ext in the range 7 – 20 MV / m. For E ext ≥ 15 MV / m, the migration velocity of the 90° DW in the direction with a positive component along the polarization vector of the extending domain was substantially higher than that in the opposite direction. The physical causes of the difference in the migration velocities of the 90° DW in the two directions were analyzed.

BaTiO3 is one of the well-known ferroelectric and piezoelectric materials, which has been widely used in various devices. However, the microscopic mechanism of the ferroelectric domain growth is not understood well. We investigated the effects of point defects, mono- and di-vacancies of Ba, Ti, and O, on the domain growth of BaTiO3 using molecular dynamics simulation with the core-shell inter-atomic potential. We found the following: ｓ(1) One kind of monovacancy, VO1, located on the TiO plane perpendicular to the applied electric field direction, acts to hinder the polarization inversion induced by the applied electric field. The monopole electric field produced by VO1 either hinders or assists the local polarization inversion in accordance with the local intensity of the total electric field. (2) The 1st-neighbor divacancies VBa-VO and VTi-VO as compared to the 2nd-neighbor divacancies asymmetrically affect the domain growth with respect to the applied electric field, making the hysteresis behavior of applied electric field vs. polarization relation. The domain grows even at a small electric field when the directions of the applied electric field and the divacancy dipole are mutually the same. (3) The domain growth speed towards the applied electric field direction is about 2 orders of magnitude higher than that towards the perpendicular direction.

In a density of states format of the frequency-extended surface-enhanced Raman spectrum, potential-induced variations of the lifetime of hydrogen bonds and their dynamic behavior were observed at aqueous solution/Au interfaces.

Silane coupling is commonly used to connect organic polymers to inorganic substrates for surface modification and composite material fabrication. It is known that the covalent bonds that form betwe...

The moving components of combustion engines are operated under harsh conditions of high pressures and temperatures. Extreme-pressure anti-wear additives, such as tricresyl phosphate (TCP), are mixed with base oil to prevent wear through the formation of a lubricant film on the substrate. We studied the effect of liquid pressure on the decomposition pathway of TCP in base oil molecules (2,5-dimethylhexane) using hybrid quantum-classical simulations with density functional theory for electrons. At a temperature of 300 K, we found that: (i) bond-breaking barrier energies of both the OC and PO bonds of TCP decrease monotonically as the liquid pressure increases; (ii) the bond-breaking barrier energy of PO is lower than that of OC at pressures of 0 and 2.0 GPa, but is higher at a pressure of 5.0 GPa; and (iii) the applied pressure significantly lowers the bond-breaking barrier energies of both OC and PO when the PO bond of TCP is directed upward from the substrate. These findings are explained by the inhomogeneous distribution of base oil molecules around TCP and the steric repulsion of the PO bond of TCP. These results indicate that the internal structures of the lubricant films are pressure-dependent.

In this study, we investigated the protonation of the amine group in epoxy resins prepared using amine-based curing agents by theoretical methods. Density functional theory (DFT)-based free-energy calculations of the corresponding deprotonation subreactions showed that the amine group of the epoxy resin is protonated at equilibrium depending on the location of the amine group when the epoxy resin is embedded in water under standard conditions. Additional DFT calculations demonstrate that the energetic barrier for breaking the ether bond of the epoxy resin is lowered by about 0.6 eV as a result of the cooperative effect of H2O dissociation and that the transition-state energy for breaking the amine group bond is lowered by about 0.4 eV after the protonation of the amine group. Comparing the transition-state energies, we predict that the bond breakage of the protonated amine groups is the principal process causing the weakening of epoxy resins under wet conditions.

A nonequilibrium molecular dynamics method is proposed to produce nonequilibrium states flexibly. In this method, virtual points are set in a simulation box, and coarse-grained physical quantities at these points are constrained using Gauss's principle of least constraint. The coarse-grained physical quantities are evaluated by averaging microscopic quantities with an appropriate weight. To obtain the weight to evaluate the coarse-grained physical quantities, a shape function matrix is initially constructed from the particle configuration. This matrix expresses an interpolation of the physical quantities at particle positions from the coarse-grained quantities at the virtual points. Then, a matrix form of the weight is calculated as the Moore-Penrose pseudoinverse matrix for the shape function matrix. This method is applied to constrain the coarse-grained kinetic energy and produce a nonuniform temperature field in the system. The temperature profile at a nonequilibrium steady state depends on the method for constructing the shape function matrix. In particular, a local temperature coincides with the coarse-grained temperature when the shape function matrix is constructed based on a higher-order interpolation.

BaTiO 3 is one of the well-known ferroelectric and piezoelectric materials, which has been widely used in various devices. However, the microscopic mechanism of the ferroelectric domain growth is not understood well. We investigated the effects of point defects, mono- and di-vacancies of Ba, Ti, and O, on the domain growth of BaTiO 3 using molecular dynamics simulation with the core-shell inter-atomic potential. We found the following: s (1) One kind of monovacancy, V O1 , located on the TiO plane perpendicular to the applied electric field direction, acts to hinder the polarization inversion induced by the applied electric field. The monopole electric field produced by V O1 either hinders or assists the local polarization inversion in accordance with the local intensity of the total electric field. (2) The 1st-neighbor divacancies V Ba -V O and V Ti -V O as compared to the 2nd-neighbor divacancies asymmetrically affect the domain growth with respect to the applied electric field, making the hysteresis behavior of applied electric field vs. polarization relation. The domain grows even at a small electric field when the directions of the applied electric field and the divacancy dipole are mutually the same. (3) The domain growth speed towards the applied electric field direction is about 2 orders of magnitude higher than that towards the perpendicular direction.

BaTiO3 is a well-known piezoelectric material, which is widely used in various devices. In general, the ferroelectric state of BaTiO3 is composed of polarized domains. The growth of these domains due to an applied electric field or stress is related to the piezoelectric performance. We investigated the effects of various point defects, monovacancies {VBa, VTi, VO}, and first- and second-neighbor divacancies {VBa–VO, VTi–VO} on polarized domain growth in BaTiO3 under an applied electric field by molecular dynamics simulations using the core–shell inter-atomic potential. We found that (i) the first-neighbor divacancy VBa–VO is the most effective in assisting the domain growth under an applied electric field (i.e., a smaller coercive electric field) in an asymmetrical manner with respect to the electric field direction. This is mainly due to the creation of an electric field around VBa–VO by significant Ti shifts toward VBa with the assistance of VO. (ii) Domain growth proceeds in a [Formula: see text] dimensional manner. The domain growth velocity in the direction of the applied electric field is approximately two orders of magnitude higher than that in the perpendicular direction. (iii) Increasing the density of the divacancy VBa–VO further lowers the coercive electric field when the applied electric field is parallel to the divacancy dipoles. The present results will be essential for designing the type, orientation, and density of defects to modify the coercive electric field of BaTiO3 in defect engineering.

The adhesive bonding of metals using epoxy resin is an important technology in manufacturing industries. It is well known that adhesion strength becomes significantly reduced in a moist environment...

The system of quinone molecules encapsulated in the single-wall carbon nanotube (SWCNT) has been proposed as a next-generation cathode electrode material for rechargeable battery. We investigate the complex interaction among the SWCNT, phenanthrene-quinone (PhQ), and Li atoms in the encapsulated system by using our original DFT code. We thereby find that the shape of the SWCNT changes significantly in the relaxed state depending on the extent of Li atoms inserted. The SWCNT shows a circular cylinder shape when no Li exists. With sufficient Li atoms inserted, the SWCNT is flattened. Substantial electron transfer from the PhQs to SWCNT is found. As for the dynamics of Li atoms in insertion or extraction process, we find that the Li atoms can take either of the two paths: one is along the inner wall of the SWCNT and the other is hopping on the PhQs.

A novel and efficient scheme for evaluating the work of adhesion between a liquid and a polymer-grafted surface is proposed. A set of spherically symmetric potentials are gradually inserted at the interface to separate the liquid molecules from the surface according to its shape. This method is applied to the interface between the water and the gold substrate modified by poly(ethylene glycol). We find that the work of adhesion becomes maximum at the intermediate density of grafted poly(ethylene glycol). This is attributed to penetration of the water molecules into grafted poly(ethylene glycol) and hydrophilic interaction between them.

Lithium (Li)-ion rechargeable batteries are indispensable for the vehicles because they have a high energy density. In a Li-ion battery, there are various key reactions and processes. This chapter describes two types of atomistic calculation methods for the large-scale simulation of Li-ion batteries. It introduces the order-N divide-and-conquer-type real-space grid density functional theory code to reduce the calculation cost of density functional theory for a large-scale model that is divided into subspaces, without degrading the accuracy. The chapter presents an application of the hybrid quantum-classical (QM-CL) simulation to elucidate the thermal diffusion process of Li ions in the graphite anode, which demonstrates how such a large-scale simulation provides physical insights into a realistic materials model. The positions of the buffer atoms are adjusted so as to minimize the potential energy under the constraint of fixing the position of the QM atoms for the CL calculation of the QM cluster region.

The validity of the molecular dynamics (MD) simulation is highly dependent on the accuracy or reproducibility of interatomic potentials used in the MD simulation. The neural-network (NN) interatomic potential is one of promising interatomic potentials based on machine-learning method. However, there are some parameters that should be determined heuristically before making the NN potential, such as the shape and number of basis functions. We have developed a new approach to select only relevant basis functions from a lot of candidates systematically and less heuristically without loosing the accuracy of the potential. The present NN potential for Si system shows very good agreements with the results obtained using ab-initio calculations.

Adhesion strength between metal and epoxy resin is well-known to reduce significantly in a moist environment. To theoretically understand its mechanisms, we calculate the shear strength of the interfacial adhesion between the surface oxidized Al and bisphenol A epoxy resin with a varying number of water molecules or hydroxide ions inserted inbetween using the hybrid quantum-classical simulation method. The quantum region in the hybrid method, which is composed of about thousand atoms at the interface, is treated by the electronic density-functional theory implemented to calculate on a real-space grid. It is thereby found that the adhesion strength reduces more significantly as the degree of the moisture content increases, in accordance with the experimental observations. Microscopic analyses find the following key features: (i) The interatomic Al–O bond between the Al atom of the oxide and the O atom of the epoxide group in the epoxy resin contributes substantially to the strength of the interfacial adhes...

We propose a method for calculating the work of adhesion between a liquid and solid surface by using molecular simulations. Two ideas are introduced for efficient calculation when the proposed method is applied at the interface between a liquid and a polymer-grafted substrate. First, the liquid molecules are separated from the solid surface based on its shape by placing spherically symmetric potentials around the atoms selected from the substrate and the polymers grafted onto it. Second, to avoid deterioration of accuracy during numerical integration of the work, the parameters that appear in the potential are updated so that variations in the gradient of the work are suppressed. This method is applied to the interface between water and a gold substrate modified by poly(ethylene oxide) (PEO), and it is found that the work of adhesion is greater at intermediate PEO densities.

Diffusion of Li-ions in graphite is an essential elementary process in the current lithium-ion battery. The C-layers of graphite deform with Li due to relatively large size of Li-ion, act to confine the Li-ions, and thereby creates correlation between them. We address theoretically the thermal diffusivity of such correlated Li-ions in graphite by the hybrid quantum–classical simulation method. In this method, the quantum-region composed of the Li-ions and surrounding C atoms is treated by the density-functional theory, while it is embedded dynamically in the total system described with an empirical inter-atomic interaction potential. We thereby take into account the long-ranged deformation field in graphite in simulating the Li-ion dynamics. Two kinds of settings of Li-ions are considered for the simulation runs at temperature 443 K : (i) seven Li-ions are inserted in the same inter-layer space of the C-layers to study their intra-plane correlation, and (ii) additional seven Li-ions are inserted in the neighboring space (i.e., fourteen Li-ions totally, 7 Li-ions in upper and 7 Li-ions in lower spaces) to study their inter-plane correlation. As for (i), the Li-ions, concentrated initially with inter-ion distances of 2.5 – 4.2 A , scatter due to their mutual Coulomb repulsion. After about 1 ps , the Li-ions and surrounding C atoms thermalize well with deformed C-layers creating a cage of radius about 13.5 A for 7 Li-ions. Diffusivity of Li-ions inside the cage is much higher than that of the cage itself. The long-time diffusion constant of the cage is the same order as that of an isolated Li-ion in graphite. As for (ii), the Li-ions, concentrated initially in the upper and lower inter-layer spaces of the C-layer, firstly form domains, and then the domains repel each other horizontally. The result is in accord with the experimental finding that the Li-rich and Li-poor planes stack in an alternating sequence in graphite.

The composite of epoxy polymers and α-alumina fillers is used as a heat dissipation material. The fillers often agglomerate with nanometer-depth polymers sandwiched in between. We address theoretically the effective thermal conductivity of such a filler-polymer-filler system. The non-equilibrium molecular dynamics simulation is performed to obtain the effective thermal conductivity of the system, in which bisphenol-A (bisA) epoxy polymer sub-system with depth 14–70 A is inserted between two α-alumina slabs. Effects of surface-coupling (SC) agent are also investigated by adding model molecules to the polymer sub-system. For smaller polymer-depth cases, the effective thermal conductivity is determined essentially by the interfacial thermal conductance that relates to the temperature-gaps at the interfaces. We find for the interfacial thermal conductance that: (i) it is decreased by decreasing the polymer depth toward the chain length of a single bisA molecule, and (ii) it is increased by adding the SC molecules to the polymer sub-system. Combining separate simulation analyses, we show that the (i) results from effectively weakened interaction between a bisA molecule and two α-alumina slabs due to the orientation constraint on the bisA molecule by the slabs. Reasons of the (ii) are enhancement of the following three quantities by addition of the SC molecules: the phonon population of the bisA molecules at those frequencies corresponding to that of acoustic phonons of α-alumina, the phonon transmission coefficient from the α-alumina slab to the polymer sub-system for the transverse acoustic phonon, and the group velocity of the transverse acoustic phonon in the polymer sub-system.

Molecular dynamics simulation has been performed to investigate the effects of irradiated helium atoms in tungsten on the bubble nucleation and the dislocation loop formation. Simulation results clearly show that helium atoms in tungsten tend to migrate as isolated interstitials at high temperatures and to be absorbed to existing tungsten-vacancies or defects such as bubbles or dislocations. Tungsten self-interstitial atoms pushed out from the helium bubble tend to stay in the vicinity of the bubble and, then form a dislocation loop when the number of the atoms exceed the threshold. Since the bubbles and dislocation loops cause further nucleation of bubbles, there appears a helium bubble array along 〈 1 1 1 〉 direction. The bubble growth rate within this self induced bubble growth mechanism will be much faster than that of existing growth model. The growth model needs to be reformulated by taking the self-induced effects into account.

The generation of tungsten fuzzy nanostructure by exposure to helium plasma is one of the important problems for the use of tungsten material as divertor plates in nuclear fusion reactors. In the present paper, the formation mechanisms of the helium bubble and the tungsten fuzzy nanostructure were investigated by using several simulation methods. We proposed the four-step process which is composed of penetration step, diffusion and agglomeration step, helium bubble growth step, and fuzzy nanostructure formation step. As the fourth step, the formation of the tungsten fuzzy nanostructure was successfully reproduced by newly developed hybrid simulation combining between molecular dynamics and Monte-Carlo method. The formation mechanism of tungsten fuzzy nanostructure observed by the hybrid simulation is that concavity and convexity of the surface are enhanced by the bursting of helium bubbles in the region around the concavity.

We performed a first-principles molecular dynamics (FPMD) simulation of the interfacial reactions between a ${\mathrm{LiCoO}}_{2}$ electrode and a liquid ethylene carbonate (EC) electrolyte. For configurations during the FPMD simulation, we also performed first-principles Co K-edge x-ray absorption near-edge structure (XANES) simulations, which can properly reproduce the bulk and surface spectra of ${\mathrm{LiCoO}}_{2}$. We observed strong absorption of an EC molecule on the ${\mathrm{LiCoO}}_{2}$ {110} surface, involving ring opening of the molecule, bond formation between oxygen atoms in the molecule and surface Co ions, and emission of one surface Li ion, while all the surface Co ions remain ${\mathrm{Co}}^{3+}$. The surface Co ions having the bond with an oxygen atom in the molecule showed remarkable changes in simulated K-edge spectra which are similar to those of the in situ observation under electrolyte soaking [D. Takamatsu et al., Angew. Chem., Int. Ed. 51, 11597 (2012)]. Thus, the local environmental changes of surface Co ions due to the reactions with an EC molecule can explain the experimental spectrum changes.

A system of quinone molecules encapsulated in single-walled carbon nanotubes (SWCNTs) has been proposed as a next-generation cathode material for rechargeable batteries [Y. Ishii et al., Phys. Chem. Chem. Phys. 18 (2016) 10411–10418]. We use density functional theory (DFT) to theoretically investigate (i) the electronic and structural states of SWCNT-encapsulated quinone with or without Li and (ii) the Li insertion and extraction dynamics in the system. Substantial electron transfer from the quinone molecules to the SWCNT is thereby observed. This electron transfer stabilizes the positively charged quinone molecules in the negatively charged SWCNT through Coulomb attraction and decreases the electronic band gap for the SWCNT with semiconductor chirality. In the case of 9,10-phenanthrenequinone (PhQ), we observe that the cross-sectional shape of the SWCNT changes substantially in the relaxed state depending on the extent of Li insertion: the SWCNT exhibits a circular cylinder shape when no Li is present, whereas it is flattened upon sufficient Li insertion. These SWCNT shapes well reflect the aggregated shapes of PhQ molecules, which depend on the amount of Li inserted. As for the Li insertion and extraction dynamics, we find that the Li atoms can take either of two paths: one is along the SWCNT wall, and the other involves hopping on the PhQ molecules and/or the sites where the C atoms of the SWCNT and the O atoms of PhQ molecules contact each other. The Li-transfer rate on the SWCNT wall is large; hence, the hopping is the rate-limiting step.

We successfully fabricated 13-kV, 20-A, 8 mm × 8 mm, drift-free 4H-SiC PiN diodes. The fabricated diodes exhibited breakdown voltages that exceeded 13 kV, a forward voltage drop of 4.9–5.3 V, and an on-resistance (RonAactive) of 12 mW·cm2. The blocking yield at 10 kV on a 3-in wafer exceeded 90%. We investigated failed devices using Candela defect maps and light-emission images and found that a few devices failed because of large defects on the chip. We also demonstrated that the fabricated diodes can be used in conducting high-voltage and high-current switching tests.

The reverse recovery characteristics of a 4H-SiC PiN diode under higher voltage and faster switching are investigated. In a high-voltage 4H-SiC PiN diode, owing to an increased thickness, the drift region does not become fully depleted at a relatively low voltage Furthermore, an electron–hole recombination must be taken into account when the carrier lifetime is equal to or shorter than the reverse recovery time. High voltage and fast switching are therefore needed for accurate analysis of the reverse recovery characteristics. The current reduction rate increases up to 2 kA/μs because of low stray inductance. The maximum reverse voltage during the reverse recovery time reaches 8 kV, at which point the drift layer is fully depleted. The carrier lifetime at the high level injection is 0.086 μs at room temperature and reaches 0.53 μs at 250 °C.

A hybrid molecular dynamics/coarse-grained-particle (MD-CGP) method is proposed for dynamic simulation of crack growth at finite temperatures. In the present method, the MD method is applied for the non-linear elastic region such as the crack tip and dislocation core, while the CGP method is applied for the surrounding linear elastic region. For coupling the atomistic and coarse regions, extra atoms and particles are placed, respectively, beyond the interface of the atomistic and coarse systems. They move according to the Langevin-type equation. The dissipation term in the Langevin-type equation contains the velocity difference between the atomistic and coarse systems. Hence, the coupling is achieved through the damped oscillation of the difference between the two systems. It is shown in a one-dimensional simulation that the present hybrid method achieves the non-reflecting boundary condition at the interface for the entire wavenumber range at finite temperatures. Two-dimensional crack growth simulations are performed using both the present hybrid MD-CGP method and full MD method for accuracy check. In the hybrid simulation, the location of the atomistic region shifts to follow the moving crack tip. In spite of such drastic operations, the results obtained by the present hybrid simulation agree very well with those by the full MD simulation. The hybrid MD-CGP method allows us to simulate very large systems without losing atomistic information at the singular point and non-linear region, with much lesser degrees of freedom than required for the full MD method.

We propose a simple method for dynamical coupling of two sub-systems with different characteristic scales described with different theoretical models, such as the fine-scale sub-system with the atomistic model (AM) such as the empirical inter-atomic potential and the coarse-scale sub-system with the coarse-grained particle (CGP) method, in a concurrent hybrid simulation scheme. Naive coupling of the different-scale sub-systems results in reflection of high wavenumber waves at the interface because of the differences in the phonon Brillouin-zone and in the dispersion relation. To solve the problem, the present scale-coupling method introduces (virtual) extra atoms and particles for the AM and the CGP sub-systems, respectively, beyond the atom-particle interface, and uses the extra atoms and the particles to mutually transfer information of the waves between the two sub-systems and to suppress the artificial reflection of the incident wave in the whole wavenumber range. As the algorithm in the present scale-coupling method is local in time and space, it is applicable to hybrid systems with any interface shape at low computation and memory requirement. Accuracy of the present scale-coupling method is compared with that of the existing methods for a simple model system. The hybrid AM-CGP simulation of indentation of a graphene nano-drum using the present scale-coupling method is performed to demonstrate its accuracy and usefulness through its comparison with the fully atomistic results..

We perform molecular-dynamics simulations to investigate the atomic and electronic structures of a basal edge dislocation in α-Al 2 O 3 . The core structure consisting of two non-stoichiometric partial dislocations, which has been recently proposed by an experiment, is examined by an empirical interatomic-potential model and by a hybrid quantum/classical approach. The atomic rearrangements in the full and in the partial dislocation cores are analyzed. The local electronic structure in the full dislocation core is evaluated by the density-functional method applied for a quantum-cluster region in the hybrid simulations. Interaction potentials between partial dislocations are investigated by the classical model. Results preliminarily obtained show that the partials aligned normal to a basal plane ({0001}) has a short-ranged repulsive nature approximately within 8 A.

Computer simulation of a variety of solid-fluid interfaces in nano-to-micrometer scales has attracted much attention in recent years. We have been developing the hybrid simulation schemes to apply them to the interfaces at realistic settings without losing physical accuracies, by concurrently coupling the electronic density-functional theory (DFT), the molecular dynamics (MD), the recursive coarse-grained particle (RCGP) method, and the lattice Boltzmann equation (LBE) method. In the hybrid DFT-MD simulation scheme, multiple DFT regions each of which is composed of a relatively small number of atoms are embedded in a system of classical MD atoms. For robust coupling of the DFT and MD regions with reasonable mechanical accuracies the buffered-cluster method is adopted, which requires no link-atoms and is applicable to a wide range of materials and settings. The sizes and number of the DFT regions change adaptively to trace the chemical reactions during the simulation run. The hybrid DFT-MD simulation scheme is successfully applied to various interesting processes including the atomic-scale friction between nano-scale objects. Useful MD simulation requires realistic, dynamic boundary conditions to the atoms. We develop the RCGP method to coarse-grain the atomic system in the solid phase, in which each particle represents a group of the atoms and the inter-particle interaction is constructed by renormalizing the inter-atomic interaction in a recursive manner under the assumption of the local statistical equilibrium. The RCGP method has attractive features such as its natural incorporation of the atomic phonons in the thermal equilibrium and its potential suitableness to connection to the atomistic system. In the hybrid RCGP-MD simulation scheme, the overall shape of the total system calculated with the RCGP method gives the dynamics boundary conditions to the MD regions. A nano-thrusting simulation of a structured Al system that demonstrates reasonable coupling of the RCGP and MD regions is presented. A hybrid RCGP-LBE simulation scheme has been developed to study interaction between the fluid motion and the elastic body in realistic settings. The dynamics of the fluid is simulated by the LBE with the dynamic boundary conditions relating to the moving solid body. The solid body is coarse-grained with the RCGP method. A hybrid RCGP-LBE simulation of a deformable nano-rod in the Poiseuille flow is performed to confirm the fluidsolid coupling scheme.

A new multiscale numerical method is developed to simulate the fluid-solid interaction. The solid motion is described by coarse grained particles which are generated by consolidation of harmonically interacting atoms, and the fluid motion is by the lattice Boltzmann method. Since the characteristic time of the fluid motion is much longer than that of the coarse grained particles, the momentum change due to the rapid collision of the coarse grained particles at the interface is accumulated over a certain time duration and then passed the fluid motion. The method is applied to an elastic rod fixed on the wall in the two dimensional Poiseuille flow. The oscillation and stress within the rod as well as the velocity and vorticity of the fluid are examined with respect to the vortex shedding at the top of the rod. Also the method is applied to the problem of fluid transfer by multiple elastic rods. It is found that the results are quite reasonable and that the present method is effective in dealing with the fluid-solid interactions.

3kV 600A 4H-SiC high temperature flat package type diodes have been developed for use in electricity supply, which are a pressure contact flat package type and include five 6mm × 6mm SiC diode chips. A developed flat package type diodes have the thermal resistance of 0.21°C/W and this value is ten times as large as silicon thermal resistance, because SiC diode chip is smaller than Si diode chip. In order to lower the thermal resistance, it is necessary to increase the number of SiC chips in the flat package because of the difficulty of a making SiC large area chip. SiC pn Flat package diode can realize the same thermal resistance value even at half chip area. The transient thermal impedance is saturated at nearly 1 seconds. On the other hand, the Si diode's transient thermal impedance is saturated at 50 seconds. In the short circuit current flows for 50ms, SiC pn Flat package diode endures the bigger pulse loads than Si diode over Tjmax of 200°C. For example SiC diode endures 2.3 times energy than Si diode at Tjmax of 500°C.

There is growing demand to perform dynamic, atomistic computer-simulation of nano-scaled interfaces. For dynamic simulation of interesting processes at the nano-interfaces, we have been developing the hybrid simulation schemes by concurrently coupling the quantum description as the electronic density-functional theory and the classical description as the classical molecular dynamics. A quantum (QM) region composed of a relatively small number of atoms, is embedded with the novel buffered-cluster method in a classical (CL) region of atoms interacting through an empirical inter-atomic potential. The hybrid QM-CL simulation scheme is applied to various kinds of nano-processes including implantation of oxygen atoms to a Si slab relating to SIMOX technology.

Feature sizes of useful electronic devices are becoming smaller and reaching nanometer ranges. There is increasing demand to perform dynamic simulations of such nano-devices with realistic sizes. To date, various kinds of simulation methods have been used for materials and devices including the density-functional theory (DFT) and the molecular dynamics (MD) for atomistic mechanics and the finite element method for continuum mechanics. We review recent progresses in our multiscale, hybrid simulation schemes that combine those methods. The coarse-grained particles (CG) method originally proposed by Rudd and Broughton [Phys. Rev. B58 (1998), p. R5893] has features suitable to such hybridization. We improve the CG method so that it is applicable to realistic nanostructured materials with large deformations. A novel hybridization scheme that couples the DFT method with the MD method is presented, which is applicable to virtually any selection of the DFT region in a wide range of materials. Hybrid DFT-MD simulations of the H2O reaction with nanostructured Si and alumina systems under stresses are performed, to demonstrate significant effects of stress on the chemical reaction.

In hybrid electronic-density-functional/molecular-dynamics schemes, a total system is partitioned in real space into the quantum-mechanical (QM) region treated by the electronic-density-functional theory and the molecular dynamics (MD) region in which atoms are interacting through the empirical inter-atomic potential. In the former hybrid scheme [Ogata et al. Comput. Phys. Commun. 149 (2002) 30], appropriate selection of QM atoms for seamless coupling between the QM and MD regions is limited in Si systems, and applications of the scheme to other materials are difficult. Novel hybrid scheme that is free from the limitation and applicable to both Si and alumina systems, is presented.