Ozaki Group

Research Subjects

  • Development of efficient methods and algorithms for first-principles electronic structure calculations
  • Development of the OpenMX software package
  • Development of first-principles methods for X-ray spectroscopies
  • First-principles calculations of two-dimensional novel structures

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 and structural materials which cannot be easily handled 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, single atom dispersion of Pt atoms, and bitriangular structure of Ge in collaboration with experimental groups. Our continuous methodological developments have been all implemented in OpenMX (Open source package for Material eXplorer).

Underlying idea of the O(N) Krylov subspace method. (1) Construction of truncated cluster for each atom. (2) Projection of the truncated subspace into a Krylov subspace. (3) Solution of the eigenvalue problem in the Krylov subspace, and back-transformation to the original space.
(a), (b) Bitriangular structure of Ge determined by DFT calculations. (c) Angle-resolved photoemission spectrum (ARPES) of the bitriangular structure. (d) Unfolded band structure of the bitriangular structure which well reproduces the ARPES measurement.

Publications and Research Highlights