ISSP - The institute for Solid State Physics

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Ozaki Group
Professor
OZAKI,
Taisuke

Research Associate
KAWAMURA,
Mitsuaki

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In accordance with development of recent massively parallel computers, first-principles calculations based on density functional theories (DFT) have been playing a versatile role to understand and design properties of a wide variety of materials. We have been developing efficient and accurate methods and software packages to extend applicability of DFT to more realistic systems as discussed in industry. Although the computational cost of the conventional DFT method scales as the third power of number of atoms, we have developed O(N) methods, whose computational cost scales only linearly, based on nearsightedness of electron. The O(N) method enables us to simulate Li ion battery, structural materials, and graphene nanoribbon based devices which cannot be easily treated by the conventional method, and to directly compare simulations with experiments. In addition to this, we have recently developed a general method to calculate absolute binding energies of core levels in solids, resulting in determination of two-dimensional structures such as silicene, borophene, and single atom dispersion of Pt atoms in collaboration with experimental groups. Our continuous methodological developments have been all implemented in OpenMX (Open source package for Material eXplorer), which has been released to public under GNU-GPL, and widely used around world for studies of a wide variety of materials.

Underlying idea of the O(N) Krylov subspace method. (1) Construction of truncated cluster for each atom by picking atoms up within a sphere. (2) Projection of the truncated subspace into a Krylov subspace. (3) Solution of the eigenvalue problem in the Krylov subspace, calculation of Green’s function associated with the central atom, and back-transformation to the original space.
XPS spectrum of silicene fabricated on ZrB2 (0001) surface by (a) experiment and (b) DFT calculation. The α-, β-, γ-peaks observed by the experiment can be identified as those from the hollow, bridge, and on-top sites, respectively. Among polymorphs caused by buckling structures, the DFT result for the planar-like structure is well compared to the experimental result.

Research Subjects

  1. Development of efficient methods and algorithms for first-principles electronic structure calculations
  2. First-principles calculations of two-dimensional novel structures
  3. Development of first-principles methods for X-ray spectroscopies
  4. First-principles calculations of superconducting critical temperature
  5. Development of the OpenMX software package