Plenary Speakers

Hiroshi Shinaoka (Saitama University)

Professor Hiroshi Shinaoka is an Associate Professor at Saitama University. His recent interest is in efficient computation related to quantum many-body theory. He has explored the sparse representation of quantities in imaginary time. There, he and his colleagues established an intermediate representation that compresses the data of functions on the Matsubara frequency lattice: from a dense Matsubara grid of size O(β) to a sparse grid of size O(logβ) (β is the inverse temperature). This makes the Matsubara summation operations and solutions of diagrammatic equations much cheaper [1].　He is also exploring more general data compression schemes using a novel concept of quantics (quantized) tensor trains  [2], which will be useful for efficient first-principles calculations as well as for revealing hidden hierarchical structures in physical quantities.

   Prof. Shinaoka is also working on the field of dynamical mean field theory (DMFT) and probably shares research interest with Prof. Held to some extent. The organizers are expecting their hot discussion.

[1] H. Shinaoka, J. Otsuki, M. Ohzeki, K. Yoshimi, Phy. Rev. B 96, 035147 (2017); Hiroshi Shinaoka, Naoya Chikano, Emanuel Gull, Jia Li, Takuya Nomoto, Junya Otsuki, Markus Wallerberger, Tianchun Wang, Kazuyoshi Yoshimi, SciPost Phys. Lect. Notes 63 (2022).

[2] H. Shinaoka, M. Wallerberger, Y. Murakami, K. Nogaki, R. Sakurai, P. Werner, A. Kauch, Phys. Rev. X 13, 021015 (2023).

Jonathan Schmidt (ETH)

Dr. Jonathan Schmidt is a young prominent researcher, currently a postdoc at ETH Zurich. He received his Ph.D. in 2022 from Martin-Luther-University Halle-Wittenberg under the supervision of Prof. Miguel Marques for his development of machine learning methods for the discovery of stable crystal structures. He has demonstrated outstanding efforts in building large-scale databases for electronic properties of materials [1][2], as well as their use for high-throughput screening of functional materials [1][3]. He also has an interest in the foundations of density functional theory, represented by his contributions to the machine-learning development of exchange-correlation functionals [4][5] and density matrix functional theory [6].

[1] J. Schmidt et al., Adv. Mater. 35, 2210788 (2023).

[2] J. Schmidt et al., Sci. Data 9, 64 (2022).

[3] J. Schmidt et al., Sci. Adv. 7, eabi7948 (2021).

[4] J. Gedeon, J. Schmidt et al., Mach. Learn: Sci. Technol. 3, 015011 (2021).

[5] J. Schmidt, M. Fadel, and C. L. Benavides-Riveros, Phys. Rev. Research 3, L032063 (2021).

[6] J. Schmidt, C. L. Benavides-Riveros, and M. A. L. Marques, Phys. Rev. B 99, 224502 (2019).

Junren Shi (Peking University)

Junren Shi, a professor at Peking University, has contributed to first-principles calculations that bridge the gap from fundamental theory to applications. His main contributions are on spin-orbit effects, Berry phase effects, and band topology effects in electronic properties [1,2,3]. Recently, he developed a first-principles method for superconductivity in liquid media that combines path integral molecular dynamics and Green's function perturbation theory [4]. This effort, as well as thermal density functional theory, could be useful for the emerging topic of high-pressure superconductivity.

[1] T. Qin, Q. Nie and J. Shi, Phys. Rev. Lett. 107, 236601 (2011).

[2] J. Shi, G. Vignale, D. Xiao and Q. Niu, Phys. Rev. Lett. 99, 197202 (2007).

[3] D. Liu and J. Shi, Phys. Rev. Lett. 119, 075301 (2017).

[4] H. Liu, Y. Yuan, D. Liu, X.-Z. Li, and J. Shi, Phys. Rev. Research 2, 013340 (2020).

Karsten Held (TU Wien)

Professor Karsten Held is a leading authority on quantum many-body theory. Although space does not allow me to present all of his research activities, I will describe some of his studies that are relevant to this workshop. He is well known as a developer of the electronic structure theory beyond the dynamical mean-field theory (DMFT) [1] and has recently done this by introducing three-body correlations to construct a nonlinear response theory [2]. This can be seen as an attempt to achieve greater precision from a higher level in the hierarchy. He is also attempting to construct a hybrid of DMFT and DFT [3] and many-body Green's function methods, such as the dynamical vertex approximation. Superconductivity is also a target of his research, and he is famous for his work on the nickelate.

[1] G. Rohringer et al., “Diagrammatic routes to nonlocal correlations beyond dynamical mean field theory”, Rev. Mod. Phys. 90, 025003 (2018).

[2] P. Kappl et al., “Nonlinear responses and three-particle correlators in correlated electron systems exemplified by the Anderson impurity model”, Phys. Rev. B 107, 20518 (2023).

[3] S. Bhandary and K. Held, “Self-energy self-consistent density functional theory plus dynamical mean field theory”, Phys. Rev. B 103, 245116 (2021).

Kieron Burke (UC Irvine)

Professor Kieron Burke is the "B" of GGA-PBE [1] and is probably one of the best-known researchers in the field of density functional theory (DFT). He has long devoted himself to the foundations of DFT. It is impossible to exhaustively list his extensive contributions, but here are a few: in 2012 [2], he led the development of exchange-correlation functionals using machine learning, pioneering subsequent progress [3]. He has also continued to pursue the semiclassical expansion of the DFT function from the Thomas-Fermi limit, revealing how quantum properties are embedded in the DFT [4]. It is noteworthy that his developments have raised the framework of orbital-free DFT to the realm of chemical accuracy [5].

[1] J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).

[2] J. C. Snyder, M. Rupp, K. Hansen, K.-R. Müller, and K. Burke, Phys. Rev. Lett. 108, 253002 (2012).

[3] L. Li, S. Hoyer, R. Pederson, R. Sun, E. D. Cubuk, P. Riley, and K. Burke, Phys. Rev. Lett. 126, 036401 (2021).

[4] P. Okun and K. Burke, "Semiclassics: The Hidden theory behind the success of DFT" in Density Functionals for Many- Particle Systems (2023).

[5] P. Okun, A. C. Cancio, K. Burke, arXiv:2304.11115.

Kiyoharu Kawana (Seoul National University)

Dr. Kiyoharu Kawana is a researcher in high energy physics. He studies the density renormalization group (RG) for its application to field theory and the B-L model, an extension of the Standard Model. Here we will briefly present only the former study. Dr. Kawana, together with Prof. Iso of KEK, has been investigating the response of classical fluids to scale transformations based on RG to study the possibility of predicting (A) thermodynamic quantities such as the equation of state and (B) the existence of nontrivial critical phenomena. The organizers hope to stimulate discussion on the relationship between this work and Dr. Takeru Yokota's approach using the functional renormalization group and Dr. Tomoaki Yagi's approach using hierarchical equations.

[1] S. Iso and K. Kawana, “Density renormalization group for classical liquids”, Prog. Theor. Exp. Phys. 2019, 013A01 (2019).

Matthias Schmidt (Universität Bayreuth)

Professor Matthias Schmidt is known for his work on soft condensed matter based on density functional theory (classical DFT). He is particularly interested in dispersions of colloidal particles and polymer solutions, collective phenomena. Recently, he has developed a novel approach called power functional theory [1] for the study of non-equilibrium physics. This theory is based on a one-body variational principle and was formulated as an extension of cDFT. The hierarchy of two- and higher-body correlation functions is accessible via the dynamical test particle limit and the non-equilibrium Ornstein-Zernike path. The theory can be applied to many phenomena, including flow in non-equilibrium steady states, kinetically induced phase separation of active Brownian particles, lane formation in binary colloidal mixtures, and steady state and transient shear phenomena.

[1] M. Schmidt, “Power functional theory for many-body dynamics”, Rev. Mod. Phys. 94, 015007 (2022).

Pablo Ordejón (ICN2)

Professor Pablo Ordejón is (with E. Artacho and J.M. Soler [1]) one of the creators, and (with many others) developer  of the SIESTA code for DFT simulations in very large systems [2]. SIESTA pioneered the field of DFT algorithms and codes with linear scaling with respect to the number of atoms in the simulation, and is widely used in the academia and the industry. He also contributed to the development of methods to deal with electronic currents in nanoscale devices (coupling DFT with Non-Equilibrium Greens Functions), implemented in the TranSIESTA code [3]. His current interests include 2D materials (specially graphene and transition metal dichalcogenides), where he has studied structural and electronic instabilities such as Charge Density Waves [4], spin-orbit effects [5], and thermal transport [6], among others. He is director of the Catalan Institute of Nanoscience and Nanotechnology (ICN2) in Barcelona (Spain), since 2012.

[1] P. Ordejón, E. Artacho and J.M. Soler, Phys. Rev. B 53, R1033 (2016).

[2] J.M. Soler et al., J. Phys,: Cond. Matt. 14, 2745 (2002);   E. Artacho et al., J Phys.: Cond. Matt. 20, 064208 (2008);  A. García et al., J. Phys. Chem. 152, 204108 (2020).

[3] M. Brandbyge, J.L. Mozos, P. Ordejón, J. Taylor, K. Stokbro, Phys. Rev. B 65, 16401 (2002).

[4] B. Guster et al., Nano Lett. 19, 3027 (2019).

[5] A. Pezzo et al., 2D Materials 9, 015008 (2021).

[6] D. Saleta Regi et al., Adv. Mat. 34, 2108352 (2022).

Ryo Nagai (Preferred Networks, inc.)

Dr. Ryo Nagai received his Ph.D. in 2023 for his work on the development of the exchange-correlation (xc) functional of DFT [1,2]. The xc functional plays a central role in DFT in mapping the electron density ρ to the energy of a system ε and the ρ-ε mapping has been developed heuristically. It can be created by machine learning the relationship of real materials, like AI does for a board game. This idea was proved for molecular systems and was extended to crystalline systems. This workshop will discuss how to improve the process for exceeding chemical accuracy.

[1] R. Nagai et al. “Neural-network Kohn-Sham exchange-correlation potential and its out-of-training transferability”, J. Chem. Phys. 148, 241737 (2018).

[2] R. Nagai et al. “Completing density functional theory by machine learning hidden messages from molecules”, npj Compt. Mater. 6, 43 (2020).

Ryosuke Akashi (National Instutes for Quantum Science and Technology (QST))

Dr. Ryosuke Akashi received his Ph.D. in 2014 for his work on the density functional theory of superconductivity, known as SC-DFT [1], although his scope extends to the many-body Green's function approach to superconductivity [2]. He is a beacon of hope for the younger generation of computational condensed-matter researchers in our country. His research is particularly focused on investigation of the relationship between Cooper pair formation and fundamental electronic properties, such as material composition, structure, density of states anomalies, plasmon [3]. He has received considerable attention for his pioneering work with Dr. Ryo Nagai in developing methodologies for constructing exchange correlation functionals using machine learning techniques. Dr. Akashi's contributions in this area have been highly regarded, further highlighting his expertise and innovative approach.

[1] R. Akashi and R. Arita, “Development of Density-Functional Theory for a Plasmon-Assisted Superconducting State: Application to Lithium Under High Pressures” Phys. Rev. Lett. 111, 057006 (2013).

[2] R. Akashi, “Revisiting the homogeneous electron gas in pursuit of the properly normed ab initio Eliashberg theory”, Phys. Rev. B 105, 104510 (2022).

[3] 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).

Sam Vinko (University of Oxford)

Primary research areas of Professor Sam Vinko are high-energy-density plasmas and X-ray free-electron lasers. His group is also working on development of theoretical methods for electronic structures and application of machine learning techniques.

   The construction of the xc function using automatic differentiation of the Kohn-Sham equation is one of their notable achievements [1]. Although training of the equation using self-consistent cycles had been proposed, its application was limited to one-dimensional systems due to its technical complexity. They extended it to real molecules in three dimensions and demonstrated its effectiveness.

   Their group has also developed a library that allows automatic differentiation of various scientific calculations [2].

[1] M. F. Kasim and S. M. Vinko, “Learning the exchange-correlation functional from nature with fully differentiable density functional theory”, Phys. Rev. Lett. 127, 126403 (2021).

[2] M. F. Kasim et al., “DQC: A Python program package for differentiable quantum chemistry”, J. Chem. Phys. 156, 084801 (2022).

Takeru Yokota (RIKEN)

Dr. Takeru Yokota has been working on a density functional theory based on the functional renormalization group (FRG-DFT). He has developed several FRG-DFT schemes applicable to (A) uniform electron gas systems [1] and (B) superconducting and superfluid systems, including condensed matter and nuclear systems. The accuracy of the energy for the uniform electron gas was found to be comparable to that obtained with the Kohn-Sham (KS) DFT combined with the local density approximation. It will be instructive to compare the FRG and KS schemes for understanding the exchange correlation functional and the hierarchical structure of the correlation functions.

   He also developed a FRG DFT scheme for classical fluids [2]. It gave a hierarchical set of equations equivalent to the BBGKY hierarchy. It will be interesting to see how the FRG-based approach differs from the schemes developed by Dr. Kawana and Dr. Yagi. The organizer expects a breakthrough from the discussion in this workshop.

[1] T. Yokota and T. Naito, “Functional-renormalization-group aided density functional analysis for the correlation energy of the two-dimensional homogeneous electron gas”, Phys. Rev. B 99, 115106 (2019).

[2] T. Yokota et al., “Functional-renormalization-group approach to classical liquids with short-range repulsion: A scheme without repulsive reference system”, Phys. Rev. E 104, 014124 (2021).

Tomoaki Yagi (RIKEN)

Dr. Tomoaki Yagi received his Ph.D. in 2022 for his work in classical density functional theory (cDFT) [1, 2]. As an introduction to Dr. Yagi, let me describe this research. The n-body direct correlation function Cn is defined as the nth functional derivative of the free energy function F with respect to density, and thus Cn is the Taylor expansion coefficient of F. This provides a non-perturbative way to describe F for a non-homogeneous system based on a homogeneous system. This requires solving a hierarchical equation known as the BBGKY hierarchy. Dr. Yagi and Prof. Sato found that all Cn can be obtained by using the weighted density approximation (WDA). They demonstrated that it is useful to apply this "self-consistent hierarchical integral equation". This is a successful overcoming of the hierarchical problem.

[1] T. Yagi and H. Sato, “Self-consistent construction of grand potential functional with hierarchical integral equations and its application to solvation thermodynamics”, J. Chem. Phys. 156, 054116 (2022).

[2] T. Yagi and H. Sato, “Self-consistent construction of bridge functional based on the weighted density approximation”, J. Chem. Phys. 154, 124113 (2021).

Yoshitaka Tanimura (Kyoto University)

Professor Yoshitaka Tanimura is well known for his work on quantum dissipative systems [1], an important topic in many areas of science, including chemical physics, biology, and statistical physics. The coupling between the system and the environment is often assumed to be weak, as in the Lindblad equation, but this is not always the case, and the coupling must be treated non-perturbatively. The problem of quantum dissipative systems can be formulated as a hierarchical equation in which the n-body correlation function is related to the m-body correlation function. Tanimura developed an algorithm to solve these equations exactly numerically. The method, called the Hierarchical Equations of Motion (HEOM) method [2], has already had a great impact on the study of quantum dissipative systems, but will have further impact on the study of other hierarchical equations that commonly appear in many-body theory.

[1] Y. Tanimura, “Stochastic Liouville, Langevin, Fokker–Planck, and master equation approaches to quantum dissipative systems”, J. Phys. Soc. Jpn. 75, 082001 (2006).

[2] Y. Tanimura, “Numerically “exact” approach to open quantum dynamics: The hierarchical equations of motion (HEOM)”, J. Chem. Phys. 153, 020901 (2020).