Akai Group

Project Professor

AKAI,Hisazumi

Our main objective is to predict/discover new functionality materials by means of computational materials design (CMD). In particular, the development of new high-performance permanent magnets is one of our main targets. CMD aims at to design materials and/or structures on the basis of quantum mechanics. This corresponds to the inverse problem of quantum simulation. In general, solving such problems is very difficult. In CMD we solve these problems by making use of the knowledge, which is obtained through quantum simulations, about underlying mechanisms realizing specific features of materials. The technique of materials information also can be exploited. In these regards, the developments of new methods of quantum simulation also are our important themes. Among them are developments of methods of accurate first-principles electronic structure calculations in general, first-principles non-equilibrium Green’s function method, order-N screened KKR-method used for huge systems, and the methods beyond LDA.

The distance dependence of exchange coupling constants J_{ij} between various atoms in Nd_{2}Fe_{14}B, which is the main component of Nd-based permanent magnets. J_{ij}’s were calculated directly using first-principles KKR-Green’s function method.

The electronic structure near the Schotkky junction formed by Al/GaN calculated by the KKR non-equilibrium Green’s function method. The local DOS as a function of the position and the energy relative to the Fermi energy is shown. The white part in the left figure corresponds to the band gap. A Schottky barrier is formed near the interface at the left. The height of the barrier is determined by the metal induced gap state (MIGS).

- First-principles electronic structure calculation
- Computational materials design (CMD)
- KKR Green's function method and its applications
- Magnetism and development of new permanent magnets

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Atomistic-model study of temperature-dependent domain walls in the neodymium permanent magnet Nd_{2}Fe_{14}B: M. Nishino, Y. Toga, S. Miyashita, H. Akai, A. Sakuma and S. Hirosawa, Phys. Rev. B **95** (2017) 094429(1-7).

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Schottky junctions studied using Korringa-Kohn-Rostoker non-equilibrium Green's function method: M. Ogura and H. Akai, J. Phys.: Condens. Matter **85** (2016) 104715(1-7).

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Relevance of 4*f*-3*d* exchange to finite-temperature magnetism of rare-earth permanent magnets: An *ab-initio*-based spin model approach for NdFe_{12} N: M. Matsumoto, H. Akai, Y. Harashima, S. Doi and T. Miyake, J. Appl. Phys. **119** (2016) 213901(1-7).

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Monte Carlo analysis for finite-temperature magnetism of Nd_{2}Fe_{14}B permanent magnet: Y. Toga, M. Matsumoto, S. Miyashita, H. Akai, S. Doi, T. Miyake and A. Sakuma, Phys. Rev. B **94** (2016) 174433(1-9).

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