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Ozaki Group

Research Associate

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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 very important role in understanding and designing 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 an O(N) Krylov subspace method, of which 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 are aiming at realization of materials design from first-principles. As a first step towards the materials design, we have been trying to develop a method to predict complicated crystal structures based on machine learning techniques. 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.
Optimized semi-coherent interface structure between BCC Fe and NbC by the O(N) method. BCC Fe (100) and NbC(100) in the NaCl structure forms semi-coherent interface structure in the Baker-Nutting relation: [010]NbC//[011]Fe, [001]NbC//[011]Fe. Iron atoms approaches to carbon atom due to strong interaction between carbon and iron atoms, resulting in that structural strain affects into the inner part of iron.

Research Subjects

  1. Development of efficient methods and algorithms for first-principles electronic structure calculations
  2. Development of first-principles electronic transport calculations
  3. First-principles calculations of two-dimensional Si structures
  4. Development of first-principles methods of core-level binding energies in solids
  5. Development of the OpenMX software package