Computer simulations from first principles enable us to investigate properties and behavior of materials beyond the limits of experiments. Our main subject is to develop and apply such methods to explain the physics of materials, to predict material properties, and to create new materials.
- Development of the transcorrelated method for condensed matter
The transcorrelated (TC) method, initially proposed by S. F. Boys and N.
C. Handy more than 40 years ago but forgotten until recently, is a wave
function theory for first-principles electronic structure calculation with
explicitly correlated wave functions. We noticed its conceptual and practical
importance and have been trying to establish the method for an alternative
of the density functional theory for years. In 2006, we reported the first
application of the TC method to the band structure calculation, but there
was a severe problem of the computational cost. After 2012, we developed
new algorithms to speed up the calculation drastically and realized its
application to various materials and extended the method for the calculation
of electronic excitation spectra also. We showed that the electronic band
structure of ZnO is reproduced best among the first-principles methods
reported so far [1].
- Development of the first-principles simulation of the thermal properties of crystals.
For the simulation of the thermal properties of crystals, a precise calculation
of the anharmonic phonon effect is necessary. A problem there is that the
spatiotemporal scale of phonon properties is diverse. So it is not easy
to simulate them by the simple application of the first-principles simulation.
We developed a method to combine first-principles molecular dynamics with
so-called sparse modeling, and established reliable calculation of the
thermal conductivity of crystals [2]. We also introduced the self-consistent
phonon approach to calculate soft phonon modes of high-temperature/high-symmetry
phases realized by the thermal fluctuation of atoms with a modest computational
cost. We applied these methods to clarify the mechanism of extremely low
thermal conductivity in a clathrate [3]. Our code (ALAMODE) is open for
the public and used by researchers in the academy and also in industry.
- Development of the Superconducting DFT code and its application to hydrogen sulfide at high pressure
In 2015, hydrogen sulfide made a record of the superconducting transition
temperature (Tc) at high pressure. The surprisingly high Tc above 200K
is explained by the phonon mechanism, on which we have contributed by the
world's first calculation of the accurate Tc with the superconducting density
functional theory (SCDFT) [4]. In this study, we used an in-house SCDFT
code we developed, for which we had made an efficient method for the Brillouin-zone
integration to improve the convergence of the calculation.
- Development of the data assimilation method to predict crystal structures
Theoretical prediction of crystal structures from its chemical composition
and physical conditions has been a long-standing problem of physical sciences.
Although there have been so many successful researches on the structural
search algorithms, the number of atoms in the unit cell reachable with
these algorithms is limited. We made a method to assimilate powder diffraction
data in the structure simulation [5]. We showed the search of complicated
crystal structures are highly accelerated even if the diffraction data
is incomplete due to the experimental constraints or the problem of the
quality of the sample. The method will support structure determination
in, for example, high-pressure experiments or materials development.
- Non-thermal laser ablation of metals by a femtosecond laser
Femtosecond laser irradiation on a metal surface changes the electron subsystem
and causes ablation without apparent thermal damage to the surrounding
area. We often call this phenomenon a non-thermal ablation, but its physical
mechanism is unclear. Based on the first-principles calculation of an electronically
high-temperature system, we proposed the electronic entropy-driven mechanism
for the ¡Ænon-thermal¡Ç ablation. We developed a simple simulation model
for ablation and succeeded in the reproduction of the ablation depth of
Copper as a function of the laser-fluence [6].
[1] M. Ochi, et al., Correlated Band Structure of a Transition Metal Oxide
ZnO Obtained from a Many-Body Wave Function Theory, Phys. Rev. Lett. 118,
026402 (2017).
[2] T. Tadano, et al., Anharmonic force constants extracted from first-principles
molecular dynamics: applications to heat transfer simulations, J. Phys.:
Condens. Matter 26, 225402 (2014).
[3] T. Tadano, et al., Impact of Rattlers on Thermal Conductivity of a
Thermoelectric Clathrate: A First-Principles Study, Phys. Rev. Lett. 114,
095501 (2015).
[4] R. Akashi et al., First-principles study of the pressure and crystal-structure
dependences of the superconducting transition temperature in compressed
sulfur hydrides, Phys. Rev. B 91, 224513 (2015).
[5] N. Tsujimoto, D. Adachi, R. Akashi, S. Todo, and S. Tsuneyuki, Crystal structure prediction supported by incomplete experimental data, Phys. Rev. Materials 2, 053801 (2018).
[6] Y. Tanaka and S. Tsuneyuki, Possible electronic entropy-driven mechanism
for non-thermal ablation of metals, Appl. Phys. Express 11, 046701 (2018).
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Methods for first-principles electronic structure calculation
- Yuansheng Zhao Ryuhei Sato and Shinji Tsuneyuki, Accelerating simulated annealing of glassy materials with data assimilation, J. Non-Cryst. Solids 600, 122028 (2022).
- Cristian M. Le, Ryosuke Akashi, Shinji Tsuneyuki, The missing quantum number
of the Floquet states, Phys. Rev. A 105, 052213 (2022)
- D. Adachi, N. Tsujimoto, R. Akashi, S. Todo and S. Tsuneyuki, Search for common minima in joint optimization of multiple cost functions, Comput. Phys. Commun. 241, 92-97 (2019)
- N. Tsujimoto, D. Adachi, R. Akashi, S. Todo, and S. Tsuneyuki, Crystal
structure prediction supported by incomplete experimental data, Phys. Rev. Materials 2, 053801 (2018).
- S. Yamada, F. Shimojo, R. Akashi, and S. Tsuneyuki, Efficient method for
calculating spatially extended electronic states of large systems with
a divide-and-conquer approach, Phys. Rev. B 95, 045106 (2017).
- M. Ochi, R. Arita, and S. Tsuneyuki, Correlated Band Structure of a Transition
Metal Oxide ZnO Obtained from a Many-Body Wave Function Theory, Phys. Rev. Lett. 118, 026402 (2017).
- M. Ochi, Y. Yamamoto, R. Arita and S. Tsuneyuki, Iterative diagonalization
of the non-Hermitian transcorrelated Hamiltonian using a plane-wave basis
set: Application to sp-electron systems with deep core state, J. Chem. Phys. 144, 4109 (2016).
- M. Ochi and S. Tsuneyuki, Second-order Moller-Plesset perturbation theory
for the transcorrelated Hamiltonian applied to solid-state calculations,
Chem. Phys. Lett. 621, 177-183 (2015).
- M. Ochi, K.Sodeyama and S. Tsuneyuki, Optimization of the Jastrow factor using the random-phase approximation and a similarity-transformed Hamiltonian: Application to band-structure calculation for some semiconductors and insulators, J. Chem. Phys. 140, 074112-1-12 (2014).
- M. Ochi and S. Tsuneyuki, Optical Absorption Spectra Calculated from a
First-Principles Wave Function Theory for Solids: Transcorrelated Method
Combined with Configuration Interaction Singles, J. Chem. Theo. Comp. 10, 4098-4103 (2014).
- M. Kawamura, Y. Gohda and S. Tsuneyuki, Improved tetrahedron method for
the Brillouin-zone integration applicable to response functions, Phys. Rev. B89, 094515 (2014).
- T. Kobori, K. Sodeyama, T. Otsuka, Y. Tateyama and S. Tsuneyuki, Trimer
Effects in Fragment Molecular Orbital-Linear Combination of Molecular Orbitals
Calculation of One-Electron Orbitals for Biomolecules, J. Chem. Phys., 139, 094113 (2013).
- M. Ochi, K. Sodeyama, R. Sakuma and S. Tsuneyuki, Efficient algorithm of
the transcorrelated method for periodic systems, J. Chem. Phys. 136, 094108(2012).
Superconductivity
- M. Kawamura, R. Akashi and S. Tsuneyuki, Anisotropic superconducting gaps
in YNi2B2C: A first-principles investigation, Phys. Rev. B 95, 4506 (2017).
- R. Akashi, W. Sano, R. Arita, and S. Tsuneyuki, Possible ¡ÈMagneli¡É Phases
and Self-Alloying in the Superconducting Sulfur Hydride, Phys. Rev. Lett. 117, 075503 (2016). Editor's Suggestion
- R. Akashi, M. Kawamura, S. Tsuneyuki, Y. Nomura, R. Arita, First-principles
study of the pressure and crystal-structure dependences of the superconducting
transition temperature in compressed sulfur hydrides, Phys. Rev. B 91, 224513 (2015).
Thermal properties
- M. Ohnishi, T. Tadano, S. Tsuneyuki, J. Shiomi, Anharmonic phonon renormalization
and thermal transport in the type-I Ba8Ga16Sn30 clathrate from first principles,
Phys. Rev. B 106, 024303 (2022).
- Y. Oba, T. Tadano, R. Akashi and S. Tsuneyuki, First-principles study of
phonon anharmonicity and negative thermal expansion in ScF3, Phys. Rev. Materials 3, 033601-1-11 (2019).
- T. Tadano and S. Tsuneyuki, Quartic Anharmonicity of Rattlers and Its Effect
on Lattice Thermal Conductivity of Clathrates from First Principles, Phys. Rev. Lett., 120, 105901-1-6 (2018).
- T. Tadano and S. Tsuneyuki, First-Principles Lattice Dynamics Method for
Strongly Anharmonic Crystals, J. Phys. Soc. Japan 87, 041015 (2018).
- T. Tadano and S. Tsuneyuki, Self-consistent phonon calculations of lattice
dynamical properties in cubic SrTiO3 with first-principles anharmonic force constatns, Phys Rev. B 92, 054301 (2015).
- T. Tadano, Y. Gohda, and S. Tsuneyuki, Impact of Rattlers on Thermal Conductivity
of a Thermoelectric Clathrate: A First-Principles Study, Phys. Rev. Lett. 114, 095501 (2015).
- T. Tadano, Y. Gohda, and S. Tsuneyuki, Anharmonic force constants extracted
from first-principles molecular dynamics: applications to heat transfer
simulations, J. Phys.: Condens. Matter 26, 225402 (2014).
Photoexcitation and laser ablation
- Cristian M. Le, Ryosuke Akashi, Shinji Tsuneyuki, The missing quantum number
of the Floquet states, Phys. Rev. A 105, 052213 (2022)
- H. Katow, R. Akashi, Y. Miyamoto, S. Tsuneyuki, First Principles Study
of the Optical Dipole Trap for Two-Dimensional Excitons in Graphane, Phys. Rev. Lett. 129, 047401 (2022).
- Y. Tanaka and S. Tsuneyuki, Possible electronic entropy-driven mechanism
for non-thermal ablation of metals, Appl. Phys. Express 11, 046701-1-4 (2018) (Spotlights 2018)
- H. Katow, J. Usukura, R. Akashi, K. Varga and S. Tsuneyuki, Numerical investigation of triexciton stabilization in diamond with multiple valleys and bands, Phys. Rev. B95, 125205 (2017).
Dielectric materials and impurities
- N. Sato, R. Akashi, and S. Tsuneyuki, Universal two-dimensional characteristics in perovskite-type oxyhydrides ATiO2H (A = Li, Na, K, Rb, Cs) , J. Chem. Phys., 147,034507(2017) .
- N. Sato and S. Tsuneyuki, Perovskite-type oxyhydride with a two-dimensional
electron system: First-principles prediction of KTiO2H, Appl. Phys. Lett. 109, 172903 (2016).
- Y. Iwazaki, Y. Gohda and S. Tsuneyuki, Diversity of hydrogen configuration
and its roles in SrTiO_{3-delta}, APL Mat. 2, 012103 (2014).
- Y. Iwazaki, T. Suzuki, Y. Mizuno and S. Tsuneyuki, Doping-induced phase
transitions in ferroelectric BaTiO3 from first-principles calculations,
Phys. Rev. B86, 214103(2012).
Magnetic materials
- Yuki K. Wakabayashi, Yoshiharu Krockenberger, Naoto Tsujimoto, Tommy Boykin,
Shinji Tsuneyuki, Yoshitaka Taniyasu and Hideki Yamamoto, Ferromagnetism
above 1000 K in a highly cation-ordered double-perovskite insulator Sr3OsO6, Nature Communications 10, 535 (2019).
- Y. Tatetsu, S. Tsuneyuki, and Y. Gohda, First-principles study on substitution effects in Nd2(Fe, X)14B, Materialia 4, 388-394 (2018).
- Y. Tatetsu, S. Tsuneyuki, and Y. Gohda, First-Principles Study of the Role
of Cu in Improving the Coercivity of Nd-Fe-B Permanent Magnets, Phys. Rev. Applied 6, 064029 (2016).
- Z. Torbatian, T. Ozaki, S. Tsuneyuki and Y. Gohda, Strain effect on the magnetic anisotropy of Y2Fe14B examined by first-principles calculations, Appl. Phys. Lett. 104, 242403-1-4 (2014).
Surface and Interface
- Y. Gohda, Y. Tatetsu, and S. Tsuneyuki, Electron theory on grain-boundary
structures and local magnetic properties of neodymium magnets, Mater. Trans., 59, 332 (2018).
- Y. Ando, Y. Gohda and S. Tsuneyuki, Dependence of the Schottky barrier
on the work function at metal/SiON/SiC(0001) interfaces identified by first-principles
calculations, Surf. Sci. 606, 1501(2012)
- Y. Ando, Y. gohda and S. Tsuneyuki, Ab initio molecular dynamics study
of the Helmholtz layer formed on solid?liquid interfaces and its capacitance,
Chem. Phys. Lett. 556, 9-12 (2012).
- Y. Gohda and S. Tsuneyuki, Structural Phase Transition of Graphene Caused by GaN Epitaxy, Appl. Phys. Lett. 100, 053111-1-4 (2012).
- Y. Gohda and S. Tsuneyuki, Two-dimensional intrinsic ferromagnetism at
nitride-boride interfaces, Phys. Rev. Lett. 106, 047201 (2011).
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