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Ryota Masuki

PhD student in Arita group, Department of Applied Physics, The University of Tokyo.

email: masuki-ryota774@g.ecc.u-tokyo.ac.jp

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github

Research interests

  • Condensed matter theory
  • Method development of first-principles calculations
  • Phonons, crystal structures, structural phase transitions
  • Finite temperature properties
  • Transport properties

Programming skills

  • C, C++
  • Python
  • Fortran
  • MPI, OpenMP

Softwares

Contributing to
  • ALAMODE
Have experience of
  • VASP
  • Quantum Espresso
  • EPW
  • Wannier90

Other softwares, etc

Developing

Publication list

Reviews and Articles
  1. 増木亮太, 野本拓也, 有田亮太郎, 只野央将 『非調和フォノン理論に基づいた有限温度における結晶構造の第一原理計算』 固体物理 2023年8月号 (in Japanese).
Preprints
Original Papers
  1. R. Masuki, T. Nomoto, R. Arita, T. Tadano "Full optimization of quasiharmonic free energy with an anharmonic lattice model: Application to thermal expansion and pyroelectricity of wurtzite GaN and ZnO" Physical Review B 107, 134119 (2023). [arXiv]
  2. R. Masuki, T. Nomoto, R. Arita, T. Tadano "Ab initio structural optimization at finite temperatures based on anharmonic phonon theory: Application to the structural phase transitions of BaTiO3" Physical Review B 106, 224104 (2022). [arXiv]
  3. R. Masuki, T. Nomoto, R. Arita, T. Tadano "Anharmonic Gruneisen theory based on self-consistent phonon theory: Impact of phonon-phonon interaction neglected in the quasiharmonic theory" Physical Review B 105, 064112 (2022). [arXiv]
  4. K. Ishihara, T. Takenaka, Y. Miao, Y. Mizukami, K. Hashimoto, M. Yamashita, M. Konczykowski, R. Masuki, M. Hirayama, T. Nomoto, R. Arita, O. Pavlosiuk, P. Wiśniewski, D. Kaczorowski, and T. Shibauchi "Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor" Physical Review X 11, 041048 (2021).
  5. R. Masuki, T. Nomoto, and R. Arita. "Origin of anomalous temperature dependence of the Nernst effect in narrow-gap semiconductors" Physical Review B 103, L041202 (2021). [arXiv]

Education

Master of Engineering, Department of Applied Physics, The University of Tokyo

March 2022

Bachelor of Science, Department of Physics, The University of Tokyo

March 2020

Fellowships

JSPS research fellow DC1

日本学術振興会 特別研究員 DC1
April 2022 ~ Present

Research Assistant, MERIT-WINGS program in the University of Tokyo

January 2021 ~ Present

Awards

Poster award

物性研究所スパコン共同利用・CCMS合同研究会「計算の時代における物性科学」
Institute of Solid State Physics, Kashiwanoha, Japan
April 2023

Master Thesis Award, Department of Applied Physics, The University of Tokyo

田中昭二賞
March 2022

Award of Faculty of Science, The University of Tokyo

理学部学修奨励賞
March 2020

Funding

Grant-in-Aid for JSPS Fellows (Grant No. 22J20892)

April 2022 ~ Present [project page]

Other contributions

Chief organizer, 66th Condensed Matter Physics Summer School

第66回物性若手夏の学校準備局代表
September 2020 ~ August 2021

Publication list

Preprints
Original Papers
  1. R. Masuki, T. Nomoto, R. Arita, T. Tadano "Ab initio structural optimization at finite temperatures based on anharmonic phonon theory: Application to the structural phase transitions of BaTiO3" Physical Review B 106, 224104 (2022). [arXiv]
  2. R. Masuki, T. Nomoto, R. Arita, T. Tadano "Anharmonic Gruneisen theory based on self-consistent phonon theory: Impact of phonon-phonon interaction neglected in the quasiharmonic theory" Physical Review B 105, 064112 (2022). [arXiv]
  3. K. Ishihara, T. Takenaka, Y. Miao, Y. Mizukami, K. Hashimoto, M. Yamashita, M. Konczykowski, R. Masuki, M. Hirayama, T. Nomoto, R. Arita, O. Pavlosiuk, P. Wiśniewski, D. Kaczorowski, and T. Shibauchi "Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor" Physical Review X 11, 041048 (2021).
  4. R. Masuki, T. Nomoto, and R. Arita. "Origin of anomalous temperature dependence of the Nernst effect in narrow-gap semiconductors" Physical Review B 103, L041202 (2021). [arXiv]

Presentations

Invited talks and seminars

  1. "非調和フォノン理論に基づく有限温度における構造最適化"
    Online CMT seminar
    April 19, 2022 (online)

  2. "Ab-initio structural optimization at finite temperatures based on anharmonic phonon theory"
    RIKEN Wednesday seminar
    March 2, 2022 (online)

Oral presentations (international)

  1. "Continuous crossover between insulating ferroelectrics and polar metals: Ab initio calculation of structural phase transitions of LiBO3 (B = Nb, Ta, W, Re, Os)"
    APS March meeting 2024
    March 4, 2024 (Minneapolis, US)

  2. "Ab initio calculation of crystal structures at finite temperatures and its application to the polar metals LiBO3"
    HIerarchical Structure and Machine Learning (HISML) 2023
    October 4, 2023 (ISSP, Kashiwanoha, Japan)

  3. "Efficient full relaxation of crystal structures with quasiharmonic approximation: Application to pyroelectricity of GaN and ZnO"
    APS March Meeting 2023
    March 7, 2023 (Las Vegas, US)

  4. "Structural optimization at finite temperature based on anharmonic phonon theory"
    APS March Meeting 2022
    March 17, 2022 (online)

  5. "Origin of anomalous temperature dependence of Nernst effect in narrow-gap semiconductors"
    APS March Meeting 2021
    March 18, 2021 (online)

Oral presentations (domestic)

  1. "非調和フォノン理論に基づく有限温度における構造最適化"
    QLC, 2nd Quantum Materials Forum
    January 6, 2023 (Tohoku University, Sendai, Japan)

  2. "熱膨張とフォノン振動数シフト計算における準調和近似の正当性と適用限界"
    日本物理学会 2021年秋季大会
    September 23, 2021 (online)

  3. "narrow-gap半導体のNernst効果の非自明な温度依存性の起源"
    日本物理学会 第76回年次大会
    March 13, 2021 (online)

Poster presentations (international)

  1. "Structural optimization at finite temperature based on anharmonic phonon theory"
    The 29th International Conference on Low Temperature Physics (LT29)
    August 23, 2022 (Sapporo, Japan)

Poster presentations (domestic)

  1. "フォノン理論に基づいた有限温度における結晶構造の第一原理計算"
    物性研究所スパコン共同利用・CCMS合同研究会「計算の時代における物性科学」
    April 3, 2023 (ISSP, Kashiwanoha, Japan)

  2. "非調和フォノン理論に基づく有限温度における構造最適化"
    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の新展開」
    May 12, 2022 (ISSP, Kashiwanoha, Japan)

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Crystal structures at finite temperatures

Self-consistent phonon (SCP) theory
The T-dependence of the free energy of the four phases of BaTiO3 [1].

The state-of-the-art structural optimization of DFT cannot be applied to the finite-temperature phases of materials because the effect of lattice vibrations is neglected. Thus, the description of structural phase transitions, which occur in a wide range of materials such as perovskites, other ferroelectrics, TMDs, etc., has been a big challenge in computational material science.

In the research, we have formulated and implemented a structural optimization theory at finite temperature, which minimizes the T-dependent free energy calculated by an anharmonic phonon theory. We have successfully reproduced the three-step structural phase transition and p-T phase diagram of BaTiO3 using the method [1].

[1] R. Masuki, T. Nomoto, R. Arita, T. Tadano "Ab initio structural optimization at finite temperatures based on anharmonic phonon theory: Application to the structural phase transitions of BaTiO3" Physical Review B 106, 224104 (2022). [arXiv]

Quasiharmonic approximation (QHA)
The thermal expansion of silicon calculated by QHA and SCP. [1].

The Quasiharmonic approximation (QHA) is the most widely used approximation in the first-principles calculation of thermal expansion. However, the validity of the approximation has been unclear because the phonon frequency shift, which is directly related to the thermal expansion by the Gruneisen formula, is not accurately reproduced in QHA.

In our research, we have shown that the quasiharmonic approximation is an accurate approximation for the thermal expansion, but not necessarily for the phonon frequency shift by comparing it with the self-consistent phonon theory. Our result validates the use of quasiharmonic approximation for calculating the thermal expansion of weakly anharmonic materials [1].

[1] R. Masuki, T. Nomoto, R. Arita, T. Tadano "Anharmonic Gruneisen theory based on self-consistent phonon theory: Impact of phonon-phonon interaction neglected in the quasiharmonic theory" Physical Review B 105, 064112 (2022). [arXiv]

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