arXiv subjects

Yoshihide Yoshimoto

Publications and source records attributed to Yoshihide Yoshimoto.

15 recordsLinked to original sources

arXiv2024

Aspect-oriented Programming with Julia

This paper proposes integrating Aspect-oriented Programming (AOP) into Julia, a language widely used in scientific and High-Performance Computing (HPC). AOP enhances software modularity by encapsulating cross-cutting concerns, such as logging, caching, and parallelizing, into separate, reusable aspects. Leveraging Julia's powerful metaprogramming and abstract syntax tree (AST) manipulation capabilities, we introduce AspectJulia, an AOP framework designed to operate within Julia's runtime environment as a package. AspectJulia enables developers to define and apply aspects seamlessly, leading to more modular, maintainable, and adaptable code. We detail the implementation of AspectJulia and present diverse use cases, ranging from HPC and scientific computing to business applications, demonstrating its effectiveness in managing cross-cutting concerns. This integration simplifies application development and improves the adaptability of existing Julia modules and packages, paving the way for more efficient and maintainable software systems.

cs.PL↗

arXiv2023

Extended Ensemble Molecular Dynamics for Thermodynamics of Phases

The first-order phase transitions and related thermodynamics properties are primary concerns of materials sciences and engineering. In traditional atomistic simulations, the phase transitions and the estimation of their thermodynamic properties are challenging tasks because the trajectories get trapped in local minima close to the initial states. In this study, we investigate various extended ensemble molecular dynamics (MD) methods based on the multicanonical ensemble method using the Wang-Landau (WL) approach. We performed multibaric-multithermal (MBMT) method to fluid phase, gas-liquid transition, and liquid-solid transition of the Lennard-Jones (LJ) system. The derived thermodynamic properties of the fluid phase and the gas-liquid transition from the MBMT agree well with the previously reported equation of states (EOSs). However, the MBMT cannot correctly predict the liquid-solid transition. The multiorder-multithermal (MOMT) ensemble shows significantly enhanced sampling between liquid and solid states with an accurate estimation of transition temperatures. We further investigated the dynamics of each system based on their free energy shapes, providing fundamental insights for their sampling behaviors. This study guides the prediction of broader crystalline materials, e.g., alloys, for their phases and thermodynamic properties from atomistic modeling.

physics.chem-ph↗

arXiv2022

Aspect-Oriented Programming based building block platform to construct Domain-Specific Language for HPC application

The world of HPC systems is changing to a more complicated system because the performance improvement of processors has been slowed down. One of the promising approaches is Domain-Specific Language(DSL), which provides a productive environment to create a high-efficient program without pain. However, existing DSL platforms themselves often lack portability and cost DSL developers great effort. To solve this issue, we propose an Aspect-Oriented Programming(AOP) based DSL constructing platform, enabling developers to build a DSL platform by combining Aspect modules. Aspect modules manage abstracted application flow, data structure, and memory access on our platform. Therefore, developers can create any DSL platform whose target application has the attributes which HPC applications usually have, the abstraction assumes. This study implemented a prototype platform that can handle MPI and OpenMP layers. The prototype supports three types of applications (Structured-Grid, Unstructured-Grid, and Particle Simulation). Then, we evaluated the overheads caused by achieving flexibility and productivity of the platform.

cs.DC↗

arXiv2021

Ab initio Derivation of Low-Energy Hamiltonians for Systems with Strong Spin-Orbit Interaction and Its Application to Ca5Ir3O12

We present an ab initio derivation method for effective low-energy Hamiltonians of material with strong spin-orbit interactions. The effective Hamiltonian is described in terms of the Wannier function in the spinor form, and effective interactions are derived with the constrained random phase approximation (cRPA) method. Based on this formalism and the developed code, we derive an effective Hamiltonian of a strong spin-orbit interaction material Ca5Ir3O12. This system consists of three edge-shared IrO6 octahedral chains arranged along the c axis, and the three Ir atoms in the ab plane compose a triangular lattice. For such a complicated structure, we need to set up the Wannier spinor function under the local coordinate system. We found that a density-functional band structure near the Fermi level is formed by local dxy and dyz orbitals. Then, we constructed the ab initio dxy/dyz model. The estimated nearest neighbor transfer t is close to 0.2 eV, and the cRPA onsite U and neighboring V electronic interactions are found to be 2.4-2.5 eV and 1 eV, respectively. The resulting characteristic correlation strength defined by (U-V)/t is above 7, and thus this material is classified as a strongly correlated electron system. The onsite transfer integral involved in the spin-orbit interaction is 0.2 eV, which is comparable to the onsite exchange integrals near 0.2 eV, indicating that the spin-orbit-interaction physics would compete with the Hund physics. Based on these calculated results, we discuss possible rich ground-state low-energy electronic structures of spin, charge and orbitals with competing Hund, spin-orbit and strong correlation physics.

cond-mat.str-el↗

arXiv2020

RESPACK: An ab initio tool for derivation of effective low-energy model of material

RESPACK is a first-principles calculation software for evaluating the interaction parameters of materials and is able to calculate maximally localized Wannier functions, response functions based on the random phase approximation and related optical properties, and frequency-dependent electronic interaction parameters. RESPACK receives its input data from a band-calculation code using norm-conserving pseudopotentials with plane-wave basis sets. Automatic generation scripts that convert the band-structure results to the RESPACK inputs are prepared for xTAPP and Quantum ESPRESSO. An input file for specifying the RESPACK calculation conditions is designed pursuing simplicity and is given in the Fortran namelist format. RESPACK supports hybrid parallelization using OpenMP and MPI and can treat large systems including a few hundred atoms in the calculation cell.

cond-mat.str-el↗

arXiv2019

Formation of 2D single-component correlated electron system and band engineering in the nickelate superconductor NdNiO2

Motivated by the recent experimental discovery of superconductivity in the infinite-layer nickelate Nd0.8Sr0.2NiO2 [Li et al., Nature 572, 624 (2019)], we study how the correlated Ni 3dx2-y2 electrons in the NiO2 layer interact with the electrons in the Nd layer. We show that three orbitals are necessary to represent the electronic structure around the Fermi level: Ni 3dx2-y2, Nd 5d3z2-r2, and a bonding orbital made from an interstitial s orbital in the Nd layer and the Nd 5dxy orbital. By constructing a three-orbital model for these states, we find that the hybridization between the Ni 3dx2-y2 state and the states in the Nd layer is tiny. We also find that the metallic screening by the Nd layer is not so effective in that it reduces the Hubbard U between the Ni 3dx2-y2 electrons just by 10--20 %. On the other hand, the electron-phonon coupling is not strong enough to mediate superconductivity of Tc ~ 10 K. These results indicate that NdNiO2 hosts an almost isolated correlated 3dx2-y2 orbital system. We further study the possibility of realizing a more ideal single-orbital system in the Mott-Hubbard regime. We find that the Fermi pockets formed by the Nd-layer states dramatically shrink when the hybridization between the interstitial s state and Nd 5dxy state becomes small. By an extensive materials search, we find that the Fermi pockets almost disappear in NaNd2NiO4 and NaCa2NiO3.

cond-mat.supr-con↗

arXiv2015

Ab initio GW plus cumulant calculation for isolated band system: Application to organic conductor (TMTSF)2PF6 and transition-metal oxide SrVO3

We present ab initio GW plus cumulant-expansion calculations for an organic compound (TMTSF)2PF6 and a transition-metal oxide SrVO3. These materials exhibit characteristic low-energy band structures around the Fermi level, which bring about interesting low-energy properties; the low-energy bands near the Fermi level are isolated from the other bands and, in the isolated bands, unusually low-energy plasmon excitations occur. To study the effect of this low-energy-plasmon fluctuation on the electronic structure, we calculate spectral functions and photoemission spectra using the ab initio cumulant expansion of the Green's function based on the GW self-energy. We found that the low-energy plasmon fluctuation leads to an appreciable renormalization of the low-energy bands and a transfer of the spectral weight into the incoherent part, thus resulting in an agreement with experimental photoemission data.

cond-mat.str-el↗

arXiv2012

Ab initio two-dimensional multiband low-energy models of EtMe_3Sb[Pd(dmit)_2]_2 and κ-(BEDT-TTF)_2Cu(NCS)_2 with comparisons to single-band models

We present ab initio two-dimensional extended Hubbard-type multiband models for EtMe_3Sb[Pd(dmit)_2]_2 and κ-(BEDT-TTF)_2Cu(NCS)_2, after a downfolding scheme based on the constrained random phase approximation (cRPA) and maximally-localized Wannier orbitals, together with the dimensional downfolding. In the Pd(dmit)_2 salt, the antibonding state of the highest occupied molecular orbital (HOMO) and the bonding/antibonding states of the lowest unoccupied molecular orbital (LUMO) are considered as the orbital degrees of freedom, while, in the κ-BEDT-TTF salt, the HOMO-antibonding/bonding states are considered. Accordingly, a three-band model for the Pd(dmit)_2 salt and a two-band model for the κ-(BEDT-TTF) salt are derived. We derive single band models for the HOMO-antibonding state for both of the compounds as well.

cond-mat.str-el↗

arXiv2010

Ab initio Low-Dimensional Physics Opened Up by Dimensional Downfolding: Application to LaFeAsO

An ab initio downfolding method is formulated to construct low-dimensional models for correlated electrons. In addition to the band downfolding by constrained random phase approximation formulated for 3D models, screening away from the target layer (chain) is further involved. Eliminating the off-target degrees of freedom, namely, dimensional downfolding yields ab initio low-dimensional models. The method is applied to derive a 2D model for a layered superconductor LaFeAsO, where the interlayer screening crucially makes the effective interaction short ranged and reduces the onsite Coulomb interactions by 10-20 \% from the 3D model for the 5 iron-3d orbitals.

cond-mat.str-el↗

arXiv2009

Melting of MgO studied using a multicanonical ensemble method combined with a first-principles calculation

Melting of MgO was studied using a multicanonical ensemble method combined with a first-principles calculation. This approach has been successively performed by using a rather simple functional form for a model inter-atomic potential that is determined from first-principles and a novel approximation treating auxiliary degrees of freedom, such as electron thermal excitations, within a multicanonical ensemble method. Although a rather simple model potential was used, this approach could distinguish differences due to the exchange-correlation potential used in the first-principles calculations. The pressure dependence of the melting point, latent heat, and volume change during melting were studied. The obtained dependence was similar to that reported by Alfe which differs from experimental results. This dependence did not change even with the PBEsol exchange-correlation potential.

cond-mat.mtrl-sci↗

arXiv2009

Ab initio Derivation of Low-Energy Model for $κ$-ET Type Organic Conductors

We derive effective Hubbard-type Hamiltonians of $κ$-(ET)$_2X$, using an {\em ab initio} downfolding technique, for the first time for organic conductors. They contain dispersions of the highest occupied Wannier-type molecular orbitals with the nearest neighbor transfer $t$$\sim$0.067 eV for a metal $X$=Cu(NCS)$_2$ and 0.055 eV for a Mott insulator $X$=Cu$_2$(CN)$_3$, as well as screened Coulomb interactions. It shows unexpected differences from the conventional extended Hückel results, especially much stronger onsite interaction $U$$\sim$0.8 eV ($U/t$$\sim$12-15) than the Hückel estimates ($U/t$$\sim$7-8) as well as an appreciable longer-ranged interaction. Reexamination on physics of this family of materials is required from this realistic basis.

cond-mat.str-el↗

arXiv2007

Optical Absorption Study by Ab initio Downfolding Approach: Application to GaAs

We examine whether essence and quantitative aspects of electronic excitation spectra are correctly captured by an effective low-energy model constructed from an {\em ab initio} downfolding scheme. A global electronic structure is first calculated by {\em ab initio} density-functional calculations with the generalized gradient approximation. With the help of constrained density functional theory, the low-energy effective Hamiltonian for bands near the Fermi level is constructed by the downfolding procedure in the basis of maximally localized Wannier functions. The excited states of this low-energy effective Hamiltonian ascribed to an extended Hubbard model are calculated by using a low-energy solver. As the solver, we employ the Hartree-Fock approximation supplemented by the single-excitation configuration-interaction method considering electron-hole interactions. The present three-stage method is applied to GaAs, where eight bands are retained in the effective model after the downfolding. The resulting spectra well reproduce the experimental results, indicating that our downfolding scheme offers a satisfactory framework of the electronic structure calculation, particularly for the excitations and dynamics as well as for the ground state.

cond-mat.str-el↗

arXiv2005

First-principles Calculation of Effective Onsite Coulomb Interaction of 3d Transition Metals: Constrained Local Density Functional Approach with Maximally Localized Wannier Function

We present a new ab initio method for calculating effective onsite Coulomb interactions of itinerant and strongly correlated electron systems. The method is based on constrained local density functional theory formulated in terms of maximally localized Wannier functions. This scheme can be implemented with any basis, and thus allows us to perform the constrained calculation with plane-wave-based electronic-structure codes. We apply the developed method to the evaluation of the onsite interaction of 3d transition-matal series. The results are discussed using a heuristic formula for screened Coulomb interactions.

cond-mat.str-el↗

arXiv2005

Nonlocal Manipulation of Dimer Motion at Ge(001) Clean Surface via Hot Carriers in the Surface States

Nonlocal one-dimensional motions of a topological defect are induced by electron tunneling through the dangling-bond states on the clean Ge(001) surface using scanning tunneling microscopy below 80 K. The direction of the motion depends both on the energy of the carriers in the surface state and on the distance between the defect and the tunneling point. The results are interpreted using an electronic excitation model by hot carriers injected to the surface states. The critical distance of the motion is anisotropic and consistent with the band structure of the surface states.

cond-mat.mtrl-sci↗

arXiv2003

Local and Reversible Change of the Reconstruction on Ge(001) Surface between c(4x2) and p(2x2) by Scanning Tunneling Microscopy

The reconstruction on Ge(001) surface is locally and reversibly changed between c(4x2) and p(2x2) by controlling the bias voltage of a scanning tunneling microscope (STM) at 80K. It is c(4x2) with the sample bias voltage V_b =< -0.7V. This structure can be kept with V_b =< 0.6V. When V_b is higher than 0.8V during the scanning, the structure changes to p(2x2). This structure is then maintained with V_b >= - 0.6V. The observed local change of the reconstruction with hysteresis is ascribed to inelastic scattering during the electron tunneling in the electric field under the STM-tip.

cond-mat.mtrl-sci↗