arXiv subjects

Yoshiro Nohara

Publications and source records attributed to Yoshiro Nohara.

8 recordsLinked to original sources

arXiv2026

Total-energy-assisted Tight-binding Method Based on Density Functional Theory - Design Principles toward Transferability and Extrapolation

The previously proposed tight-binding method derived from the total energy has been extended within the local density approximation (TE-TB method; J. Phys. Soc. Jpn. 87, 064802 (2018)). Unlike the earlier two-parameter formulation, the present method introduces three parameters. These parameters explicitly capture local packing effects and improve transferability. Furthermore, based on physical considerations, several boundary conditions (inductive bias) are imposed on the functionals defining the tight-binding Hamiltonian and related energy functionals. The revised formalism is tested on crystalline silicon to assess the stability of the diamond structure, a monovacancy, and the (001) surface. These benchmark tests demonstrate the high transferability and reliability of the present three-parameter TE-TB design philosophy.

cond-mat.mtrl-sci↗

arXiv2019

Wannier90 as a community code: new features and applications

Wannier90 is an open-source computer program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch states. It is interfaced to many widely used electronic-structure codes thanks to its independence from the basis sets representing these Bloch states. In the past few years the development of Wannier90 has transitioned to a community-driven model; this has resulted in a number of new developments that have been recently released in Wannier90 v3.0. In this article we describe these new functionalities, that include the implementation of new features for wannierisation and disentanglement (symmetry-adapted Wannier functions, selectively-localised Wannier functions, selected columns of the density matrix) and the ability to calculate new properties (shift currents and Berry-curvature dipole, and a new interface to many-body perturbation theory); performance improvements, including parallelisation of the core code; enhancements in functionality (support for spinor-valued Wannier functions, more accurate methods to interpolate quantities in the Brillouin zone); improved usability (improved plotting routines, integration with high-throughput automation frameworks), as well as the implementation of modern software engineering practices (unit testing, continuous integration, and automatic source-code documentation). These new features, capabilities, and code development model aim to further sustain and expand the community uptake and range of applicability, that nowadays spans complex and accurate dielectric, electronic, magnetic, optical, topological and transport properties of materials.

cond-mat.mtrl-sci↗

arXiv2016

Interpolation across a muffin-tin interstitial using localized linear combinations of spherical waves

A method for 3D interpolation between hard spheres is described. The function to be interpolated could be the charge density between atoms in condensed matter. Its electrostatic potential is found analytically, and so are various integrals. Periodicity is not required. The interpolation functions are localized structure-adapted linear combinations of spherical waves, socalled unitary spherical waves (USWs), centered at the spheres where they have cubic-harmonic character. Input to the interpolation are the coefficients in the cubic-harmonic expansion of the target function at and slightly outside the spheres; specifically, the values and 3 first radial derivatives. To fit this, we use USWs with 4 negative energies. Each interpolation function is actually a linear combination of these 4 sets of USWs with the following properties: (1) It is centered at a specific sphere where it has a specific cubic-harmonic character and radial derivative. (2) Its value and first 3 radial derivatives vanish at all other spheres and for all other cubic-harmonics. It is therefore highly localized. Explicit expressions are given for these value-and-derivative (v&d) functions and their Coulomb potentials in terms of the USWs and their structure matrix, including those with zero energy, as well as for integrals over the interstitial of the v&d functions and of their products. Use of point- and space-group symmetries can significantly reduce matrix sizes and the number of v&d functions. For open structures, additional constraints are needed to pinpoint the interpolated function deep in the interstitial. This requires the USW set at one extra energy. As examples, we consider a constant density and the valence-electron densities in zinc-blende structured Si, ZnSe, and CuBr.

cond-mat.mtrl-sci↗

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↗

arXiv2011

Ab initio Derivation of Correlated Superatom Model for Potassium Loaded Zeolite A

We derive an effective low-energy Hamiltonian for potassium loaded zeolite A, a unique ferromagnet from non-magnetic elements. We perform ab initio density functional calculations and construct maximally localized Wannier functions for low-energy states made from potassium s electrons. The resulting Wannier orbitals, spreading widely in the alminosilicate cage, are found to be the superatomic s and p orbitals in the confining potential formed by the host cage. We then make a tight-binding model for these superatomic orbitals and introduce interaction parameters such as the Hubbard U. After mean-field calculations for the effective model, we find that ab initio spin density functional results are well reproduced by choosing appropriate sets of the interaction parameters. The interaction parameters turn out to be as large as the band width, $\sim$ 0.5 eV, indicating the importance of electron correlation, and that the present system is an interesting analog of correlated multi-orbital transition metal oxides.

cond-mat.str-el↗

arXiv2011

Twelve-dimensions theory in electromagnetic dynamics as a hypothesis

We propose a theory in electromagnetic dynamics, in which time and space are equivalent with each other and have totally twelve dimensions. Then, we solve that with realistic assumptions and find a steady state as a solution. The solution draws a circle in complex space having six dimensions as a closed string, which is an orbit passed by waves of two scalar fields having electric and magnetic characters, respectively. We also discuss a possibility of existing solutions of electromagnetic waves.

physics.gen-ph↗

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

Spin density functional study on magnetism of potassium loaded Zeolite A

In order to clarify the mechanism of spin polarization in potassium-loaded zeolite A, we perform {\em ab initio} density-functional calculations. We find that (i) the system comprising only non-magnetic elements (Al, Si, O and K) can indeed exhibit ferromagnetism, (ii) while the host cage makes a confining quantum-well potential in which $s$- and $p$-like states are formed, the potassium-4$s$ electrons accommodated in the p-states are responsible for the spin polarization, and (iii) the size of the magnetic moment sensitively depends on the atomic configuration of the potassium atoms. We show that the spin polarization can be described systematically in terms of the confining potential and the crystal field splitting of the p-states.

cond-mat.str-el↗