# COLLOQUIA 2019

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 42513:30 ItoTanaka My self-introductionTo introduce myself 5913:30 HamaguchiKotaka First-Principles Study on Cathode Properties of Ti, Cr, and Mn-based Cation-Disordered OxidesBattery Performance and Reaction Mechanism in Tin compounds as Negative Electrode: First-Principles Calculation 51613:30 KurodaHayashi Spin injection into semiconducting system with Heusler alloys by first-principles calculationsAnalysis of crystal structural stability of transition-metal compounds by using machine learning method 52313:30 DucHung P2 Layer Oxides AxMO2Magnetocaloric effect of MnCoGe base alloy 53013:30 TakahashiMatsumiya Conversion-Type Reaction Mechanism Analysis of Li-Ion Battery Cathode Material FeF3 by First-Principles CalculationsThe review of gElectric-field-induced of magnetic moments and magnetocrystalline anisotropy in ultrathin cobalt filmsh 6613:30 HuyenKatsumoto Piezoelectricity in Multiferroic Bismuth Oxides. 61313:30 Shimazu Materials design of hetero interface showing spin-valley topological phase by first-principles calculations 62015:30 YamashitaFujii Crystal Structure Prediction by Bayesian Optimization and Evolutionary AlgorithmIntroduction to LIDG program 62713:30 FujimuraMakinoFukushima Thermoelectric property of SnSe using GW calculationThe differences of research between in company and in universityScale-brigding methods for dilute magnetic systems 7413:30 MomidaMasagoHamada First-principles calculations of ZnO nanostructuresGa-vacancy-enhanced ferromagnetism in Eu-doped GaNDevelopment of Program code for the first-principles photoemission-spectrum calculation 71113:30 DanilaThaoYamauchi First-principles approach to novel 2D ferromagnetsElectric-field effect on magnetocrystalline anisotropy in 3d transition-metal thin films.Wannier-function description of the electronic polarization in lacunar spinels 71813:30 ShiraiOguchi State Variables and Constraints in Thermodynamics of SolidsPrecision of All-Electron FLAPW Method- Continuing Development of HiLAPW -

### 2019Nx

Title : My self-introduction

Speaker : Kazuki Ito

Abstract:

I would like to talk about my profile.

Title : To introduce myself

Speaker : Yuki Tanaka

Abstract:

I would like to introduce myself.

Title : First-Principles Study on Cathode Properties of Ti, Cr, and Mn-based Cation-Disordered Oxides

Speaker : Motoyuki Hamaguchi

Abstract:

Li-ion batteries (LIBs) are widely used for energy storage devices because they have high voltage, high energy densities, and high capacities. However, typical cathode material LiCoO2 for LIBs include expensive and highly toxic rare metal Co. Therefore, We have investigated alternative cathode oxides based on Ti, Cr, and Mn-based cation-disordered oxides Li1.2M1_0.4_M2_0.4_O2 (M1, M2 = Ti, Cr, and Mn). In this talk, we present first-principles study focused on their cathode properties.

Title : Battery Performance and Reaction Mechanism in Tin compounds as Negative Electrode: First-Principles Calculation

Speaker : Hiroki Kotaka

Abstract:

In the modern society, the rechargeable-ion batteries have been widely utilized as energy storages in various types of electronic devices. The demand for applications of the rechargeable-ion batteries is becoming larger, and its application ranges are also spreading to power sources of electric vehicles and large-scale electric-power storage systems. To overcome to increased demand, it is necessary to develop new electrode materials without high-cost rare-metals. We investigate the battery characteristics of SnS and Sn_4P_3 as a negative electrode for rechargeable battery by first-principles calculations. We calculate a phase diagram of ternary systems from formation energy, and clarify a possible reaction route considering intermediate products in discharge reactions. We calculate the voltage-capacity curves based on the reaction path obtained from the ternary phase diagram. To evaluate the battery performance, we compare the storage performance of Li and Na ion.

Title : Spin injection into semiconducting system with Heusler alloys by first-principles calculations

Speaker : Fumiaki Kuroda

Abstract:

Recently development of spin-transistor technology has been increasingly demanded, because it can realize nonvolatility, reconstructibility, and ultralow power consumption for the electronic devices. High spin-polarized current into semiconductors and semimetals is the key for implementation of this transistor. Some Heusler alloys are expected to generate fully spin-polarized current resulting from half-metallic states. Therefore, spin injection into semiconductors with Heusler alloys has attracted much attention. In this talk, we discuss the origin of large magneto-resistive (MR) effect in Co2FeAl0.5Si0.5/Ge which was observed in experiment. First of all, we introduce basic theory of ballistic transport for understanding the origin of MR effect. Then, we show the results of ballistic transport calculations for Fe/MgO (001) and Fe/Ge (111) to tell the importance of band symmetry matching and band-folding effect. Finally, we discuss spin transport properties of Co2FeAl0.5Si0.5/Ge and Co2FeAl0.5Si0.5/Fe(5)/Ge.

Title : Analysis of crystal structural stability of transition-metal compounds by using machine learning method

Speaker : Takafumi Hayashi

Abstract:

Recently, material informatics(MI) has attracted much attention. MI is the field that utilize machine learning for material science. It is used to predict physical properties of unknown materials, or to determine dominant variables of properties. Our aim is to understand dominant factors of mechanical properties of MB, MC, and MN (M : 3d, 4d, and 5d transition-metals) by using the technique of MI. These transition-metal compounds are candidates for hard materials which are used for cutting tools, wear resistance parts and so on. Data about physical properties of transition metal compounds can be obtained by the first-principles calculations[1]. As the first step, we have performed a linear regression analysis of formation enthalpy of the transition-metal compounds by using the linearly independent descriptor generation (LIDG) method. By using LIDG method, we can get a simple and high performance model. In this talk, I would like to talk and discuss about our regression analysis.
[1] M. Fukuichi, H. Momida, M. Geshi, M. Michiuchi, K. Sogabe, and T. Oguchi, J. Phys. Soc. Jpn. 87, 044602 (2018).

Title : Magnetocaloric effect of MnCoGe base alloy

Speaker : Tran Ba Hung

Abstract:

Air cooling and refrigeration have become essential of life. However, the current method using compressible gas leads to some certain harmfulness because of greenhouse gas. The use of magnetocaloric effect is promising for a future cooling system instead of traditional methods causing ozone depletion and global warming. Magnetocaloric effect is an intrinsic property of magnetic materials where temperature of magnetic material is changed when applying and shutting down magnetic field. In this work, we study the magnetism of MnCoGe based alloys, which have attracted much attention in recent experiments because of giant entropy change at room temperature. The Curie temperature and other properties obtained in this work are in good agreement with available data[1]. We also discuss about doping effect on Curie temperature on the basis of the present theoretical findings.
[1] Yulong Shen et al, Mater. Res. Express 4, 116110 (2017)

Title : P2 Layer Oxides AxMO2

Speaker : Luong Huu Duc

Abstract:

P2 Layer Oxides AxMO2 was known as good cathode materials with high voltage and capacity for Lithium Ion Batteries (LIBs). However, the deficiency of lithium in the context of highly increasing energy storage demand leads to investigation of new replaceable elements as charge carrier with similar lithium ionfs properties.1 Recent study pointed out that Sodium-based compounds would be a promising alternative with a similar voltage and capacity. However, diffusion mechanism of Sodium inside materials has not been clear since factors influencing on Na diffusion have not included systematically. Here, we systematically investigate the geometric and electronic structure, Na ordering with mixed M4+/M3+ arrangement as long as the diffusion mechanism of Sodium in a low cost material NaxMnO2 (0< x <1) using Density Functional Theory Method. Since GGA could not describe exactly the d orbital of transition metal, the Hubbard U parameter (U=4.0) was employed. In the geometric structure of NaxMnO2, Na ions can locate at face-shared sites (Naf) and edge-shared sites (Nae). The stability diagram illustrates that the arrangement of Na ion at a concentration x = 1/2 reaches the most stable one. The ground state has only Nae sites occupied while structure with x = 1/3 and 2/3, Na ion can locate in both sites. Our calculation shows that this material possessing a high voltage, in the range from 2.0 to 3.5V, would be promising to apply for portable devices. When a Na ion is deintercalted from NaMnO2, we found evidence that an Mn3+ ion at the second nearest neighbour (2NN) of Na vacancy would be oxidized to be Mn4+. The bond length shrinkage, bound states appeared near the Fermi level and magnetic moment reduction indicate a small polaron formed at 2NN site. The polaron migrates simultaneously with the Na ion diffusion. The diffusion of small polaron Na vacancy complex was described by two elementary diffusion processes (EDPs), crossing and parallel processes. The crossing and parallel elementary diffusion process occur when a small polaron diffused crossingly (parallelly) with Na ion diffusion. Both elementary diffusion processes require almost the same activation energy of approximately 410 meV. Compared with the other materials such as LiFePO4 (430 meV), NaVOPO4 (395 meV), this material would be promising material for cathode of Sodium Ion Batteries.

Title : Conversion-Type Reaction Mechanism Analysis of Li-Ion Battery Cathode Material FeF3 by First-Principles Calculations

Speaker :

Abstract:

Li-ion battery (LIB) is among the rechargeable batteries with high capacity, high voltage, and high cyclability, and used in many of mobile applications, vehicles, and natural power generations. Perovskite-type FeF3 is one of the most promising cathodes for Li-ion batteries because of its much higher capacity than LiCoO2. However, its capacity is rapidly lost during discharge-charge cycles, and its reaction mechanism has not been completely revealed. In the previous works[1,2], x-ray absorption spectroscopy (XAS) spectra at the Fe K edge and its voltage profile during discharge-charge cycles were measured for compounds appearing in the reactions. From these measurements and analyses, the reaction path during the discharge process is presumed with the change of crystal structures along the increase of Li concentration, which is firstly the insertion reaction between the interatomic gaps of FeF3, and secondly the conversion reaction to two phases: Fe and LiF[2]. In this study, we assume the reaction path during the discharging process as models (Fig. 1). Magnetic structures are assumed to be antiferromagnetic (AFM) for iron fluorides, ferromagnetic (FM) for metallic iron, and nonmagnetic (NM) for others. Using this model, we first evaluate the formation energy during the discharge process with density-functional-theory calculations within generalized gradient approximation (GGA) and GGA+U. In GGA, the obtained discharging reaction has two steps as FeF3 + 3Li Li0.5FeF3 + 2.5Li Fe + 3LiF, and in GGA+U, by contrast, it has three steps as FeF3 + 3Li Li0.5FeF3 + 2.5Li FeF2 + LiF + 2Li Fe + 3LiF. From these reaction paths, we then reproduce the voltage profiles and the XAS spectra at the Fe K edges with GGA+U, being in a good agreement with experiments. Finally, we analyze the density of states and reveal that GGA+U calculations explain well the change of ionic valences on Fe atoms during discharging process.
References:
[1] A. Kitajou, I. Tanaka, Y. Tanaka, E. Kobayashi, H. Setoyama, T. Okajima, S. Okada, Electrochemistry 85, 472 (2017).
[2] L. Li, R. Jacobs, P. Gao, L. Gan, F. Wang, D. Morgan, S. Jin, J. Am. Chem. Soc. 138, 2838 (2016).

Title : The review of gElectric-field-induced of magnetic moments and magnetocrystalline anisotropy in ultrathin cobalt filmsh

Speaker : Ryuta Matsumiya

Abstract:

Although using magnetic field induced by electric current to change the direction of magnetization is common, its energy consumption is not negligible due to Joule heating. Electric field induced magnetic anisotropy change is attracting the attention to solve such problem. This is called voltage-controlled magnetic anisotropy (VCMA). In this study, the microscopic origins of the VCMA in 3dferromagnetic metals are revealed. Using in situ x-ray uorescence spectroscopy that provides a high quantum ef ciency, electric eld induced changes in orbital magnetic moment and magnetic dipole terms in ultrathin Co lms are demonstrated. An orbital magnetic moment difference of 0.013 muB was generated in the presence of electric elds of + or -0.2V/nm. The VCMA of Co was properly estimated by the induced change in orbital magnetic moment, according to the perturbation theory model. The induced change in the magnetic dipole term only slightly contributed to the VCMA in 3d-ferromagnetic metals. Recent research has shown the significance of the magnetic dipole term in 5d state to the VCMA in Pt with proximity induced spin polarization.
[1] T. Kawabe et al, Phys. Rev. B 96, 220412(R) (2017)

Title : Piezoelectricity in Multiferroic Bismuth Oxides

Speaker : Hiroshi Katsumoto

Abstract:

The piezoelectricity is the change of an electric polarization by strain or pressure. The best material is PbZrxTi1-xO3 (PZT), which shows highest piezoelectric coefficients at x = 0.5. However, Lead-free piezoelectric materials are desired because of the toxicity of Lead. The perovskite solid solution Bi(Fe,Co)O3, which is composed of BiFeO3 and BiCoO3, which show R3c rhombohedral and P4mm tetragonal structure, respectively, has attracted much attention as promising multiferroic material showing the large electric polarization at room temperature and a candidate for a lead-free piezoelectric material because the phase diagram has the similarity to that of PZT [1]. BiFeO3 is a representative multiferroic material showing both ferroelectricity and G-type antiferromagnetism [2]. On the other hand, BiCoO3 shows pyroelectricity with high tetragonality and C-type antiferromagnetism. The spontaneous electric polarization evaluated by using DFT calculation was 179 muC/cm2 [3]. BiFe1-xCoxO3 shows several structural phase transitions varying the solubility, x. The morphotropic phase boundary (MPB) was discovered in BiFe1-xCoxO3 around 0.2 < x < 0.4 at room temperature, where monoclinic phase is present [4]. The enhancement of piezoelectric coefficient and polarization rotation is expected to be in the vicinity of the MPB. In order to evaluate the piezoelectricity and the magnetic stability, we performed first-principles calculations based on a Fe/Co chemically ordered model of BiFe2/3Co1/3O3. The monoclinic Cm structure has \sqrt(2)x\sqrt(2)x1 supercell and expected to show ferrimagnetism. The Neel temperatures was also evaluated within the mean-field approximation by using the exchange integrals which was obtained by projecting the DFT energy of several magnetic configurations to a classical Heisenberg model. Since our supercell has four sublattices regarding the magnetic ions, the Neel temperatures is obtained by diagonalizing the magnetic matrix. As presenting the results, we will discuss the electronic response to ferroelectric distortion and macroscopic mechanism of the magnetic stability in Bi(Fe,Co)O3.

[1] M. Azuma et al., Jpn. J. Appl. Phys. 47, 7579 (2008).
[2] G. Catalan et al., Adv. Mater. 21, 2463 (2009).
[3] Y. Uratani et al., Jpn. J. Appl. Phys. 44, 7130 (2005).
[4] K. Oka et al., Angew. Chem. Int. Ed. 51, 7977 (2012).
[5] P. W. Anderson, Theory of Magnetic Exchange Interactions, in Solid State Physics, edited by F. Seitz and Turnbull, Vol. 14 (1963).

Title :

Speaker :

Abstract:

Title : Materials design of hetero interface showing spin-valley topological phase by first-principles calculations

Speaker : Ryoma Shimazu

Abstract:

As an electronic degree of freedom, spin-valley-tronics, which uses the freedom of the valley, is attracting attention in addition to charge and spin. The valley refers to the characteristic band structure of a unique mountain shape appearing at the top of the valence band (or the bottom of the conductor) at the end of the Brillouin zone. In a monolayer of transition metal dichalcogenide MoS2, spin splitting (spin-valley coupling) occurs in the valley from the breaking of space inversion symmetry, valley degrees of freedom can be controlled by the left and right circular polarization of light [1]. Also, 2D honeycomb lattices such as Sn and Bi are buckling due to strong spin-orbit interaction, and are known to be 2D topological insulators [2]. Our purpose is to theoretically design interfaces that simultaneously exhibits spin-valley coupling and topological edge states and to search for materials applicable to a new device field (Spin Valley Electronics) utilizing spin-valley. In this research, using first principles calculation, we calculated the band structure of hetero interface by combination of transition metal dicargogenide and 2D topological insulator. I will discuss changes in band structure due to changes in stacking of layers or matters.
[1] D. Xiao et al., Phys. Rev. Lett. 108, 196802 (2012).
[2] M. Ezawa, J. Phys. Soc. Jpn. 84, 121003 (2015).

Title : Crystal Structure Prediction by Bayesian Optimization and Evolutionary Algorithm

Speaker : Tomoki Yamashita

Abstract:

Crystal structure prediction methods such as random search (RS) and evolutionary algorithm (EA) have attracted attention. Previously we have developed a searching algorithm accelerated by Bayesian optimization (BO). BO is a selection-type algorithm which can efficiently select potential candidates by machine learning. First, we compared searching efficiency among RS, EA, and BO in the small system of Si16. In each algorithm, a hundred structures were searched. The importance of random generation is found compared with evolutionary operations even in EA. RS could be the most efficient for small systems. Furthermore, we develop a hybrid algorithm of BO and EA, and discuss the searching efficiency in large systems.

Title : Introduction to LIDG program

Speaker : Hitoshi Fujii

Abstract:

I will introduce the recently released LIDG (https://github.com/Hitoshi-FUJII/LIDG) code.

Title : Thermoelectric property of SnSe using GW calculation

Speaker : Takayoshi Fujimura

Abstract:

We aim at development of calculation tool of thermoelectric material and construction of data base. We searched for thermoelectric materials using high precision GW calculation method. We focused on SnSe which is one type of chalcogen compound. As an index for evaluating thermoelectric materials, ZT expressed by Seebeck coefficient, electric conductivity and thermal conductivity is used. In the experiment, SnSe undergoes a phase transition at 807K, and ZT = 2.6 at 923K of the high temperature phase[1]. Since this value is currently the highest level, SnSe is expected as a new thermoelectric material. In this presentation, We introduce the Seebeck coefficient of SnSe obtained from the highly accurate electronic structure by GW calculation.
[1] L. D. Zhao et al., Nature (London) 508, 373 (2014)

Title : The differences of research between in company and in university

Speaker : Yukihiro Makino

Abstract:

I will talk about the differences of research between in company and in university. Most difference is the purpose, I think. In company we must make products and sell them, at the end of research activities. All themes in company are relating to products, for example, to make them better, stronger, or make production process easier, yielding rate improved, etc. I will show you more different points.

Title : Scale-brigding methods for dilute magnetic systems

Speaker : Tetsuya Fukushima

Abstract:

Multi-scale simulations (scale-brigding methods), consisting of first-principles calculations and model calculations, are quite useful for investigating the electronic structure and magnetic properties in dilute magnetic systems. Ifll give a brief introduction of the mauti-scale simulation techniques.

Title : First-principles calculations of ZnO nanostructures

Speaker : Hiroyoshi Momida

Abstract:

We have performed the first-principles calculations of zinc oxide nanostructures including nanowires and nanosheets. We focus our attention especially on atomistic structures and piezoelectric properties of the materials. As a result, piezoelectric constants of nanowires can increase as diameters decreases in a range of 0.3-1.7 nm. It is found that atomic structures in nanosheets significantly depend on thicknesses and in-plane strains.

Title : Ga-vacancy-enhanced ferromagnetism in Eu-doped GaN

Speaker : Akira Masago

Abstract:

Eu-doped GaN is a luminescent and ferromagnetic material, and this is a promising material for spintronics. It is computationally demonstrated that room-temperature ferromagnetism, which has been experimentally observed, is induced by holes in N 2p states (i.e., Zener's double exchange interaction) that arise from Ga vacancies as a result of the introduction of Eu ions (i.e., volume compensation). In this presentation, I show the Curie temperature increases with increasing concentration of not only Eu ions but also Ga-vacancies.

Title : Development of Program code for the first-principles photoemission-spectrum calculation

Abstract:

I am developing a program code for calculating the photoemission spectrum. The spectrum is calculated by using the partial density of states (PDOS) and the atomic photoionization cross section. In the hard x-ray photoemission experiment, the photoelectron intensity is very much enhanced for the s state. A preliminary result is shown for CuAlO2 delafossite.

Title : First-principles approach to novel 2D ferromagnets

Speaker : Danila Amoroso

Abstract:

Title : Electric-field effect on magnetocrystalline anisotropy in 3d transition-metal thin films.

Speaker : Nguyen Thi Phuong Thao

Abstract:

Recently, electric-field control of magnetocrystalline anisotropy (MCA) in thin films has attracted much attention in the field of spintronics as a key phenomenon to reduce the energy consumption in MRAM [1]. This phenomenon was observed in magnetic tunnel junction consisting of 3d transition-metal thin films is considered to become a key element of the current MRAM technology. The electric-field-induced modification of the MCA in itinerant thin film ferromagnets has been demonstrate experimentally [2], in ultranthin Co films. In this study, we propose first principles calculations on effect of electric field on magnetism in Co thin film. Calculations carried out for 5 layers pure Co and Ni/Co thin films will be shown in this talk.
[1] D. Chiba, M. Yamanouchi, F. Matsukura, and H. Ohno, Science 301, 943 (2003).
[2] T. Kawabe el at Phys. Rev. B 96, 220412 (2017).

Title : Wannier-function description of the electronic polarization in lacunar spinels

Speaker : Kunihiko Yamauchi

Abstract:

Recently, magnetic lacunar spinels, such as GaV4S8, GaV4Se8, and GaMo4S8, were proposed to exhibit skyrmion phases under magnetic field. Apart from skyrmion, the multiferroicity can also emerge in this system, where the ferroelectric polarization is driven by Jahn-Teller distortion of the tetrahedra formed by transition-metal ions. In this talk, I will introduce Wannier function as a tool to describe the electronic polarization and discuss the polarization developed as a function of Coulomb interaction U.
Ref. Hui-Min Zhang, et al., Phys. Rev. B 99, 214427 (2019).
https://doi.org/10.1103/PhysRevB.99.214427

Title : State Variables and Constraints in Thermodynamics of Solids

Speaker : Koun SHIRAI

Abstract:

There is a common view in thermodynamics that the behavior of a macroscopic system can be described by only a few state variables. Although this is true for many cases, it is unclear whether it is meaningful to ask how many state variables are acceptable. This is indeed a problem when solids are investigated within the framework of thermodynamics. The present study gives an answer to this question: the mean values of all the atom positions of a given solid together with the internal energy constitute a commensurate set of state variables (thermodynamic coordinates, abbreviated as TCs). This conclusion is a rigorous consequence of the the second law. The full set of TCs enables us to treat disordered solids, which are traditionally considered to be nonequilibrium states so that the standard thermodynamic methods cannot be applied, completely within equilibrium thermodynamics. The configuration entropy and the change in entropy in phase transitions can be described in terms of the degeneration in the set of TCs. A few working examples of TCs in solids are given.

Title : Precision of All-Electron FLAPW Method- Continuing Development of HiLAPW -

Speaker : Tamio Oguchi

Abstract:

Accuracy and precision are two ways that scientists think about error. Accuracy refers to how close a measurement is to the true or accepted value. Precision refers to how close measurements of the same item are to each other. It is now widely realized that first-principles calculations have important role to generate bigdata in materials informatics. Thus, precision evaluation and control in the first-principles calculations have become crucial for better data generation and collection in addition to the improvement of their accuracy. A recent research article about "Reproducibility in density functional theory calculations of solids" [1] made impact in this context. In this Colloquium, key factors determining the precision in the all-electron full-potential linearized augmented plane wave method are revisited and their appropriate values and numerical treatment are examined with test data taken from Ghiringhelli's paper [2] for 82 octet elementary and binary semiconductors with main-group elements.
[1] K. Lejaeghere et al., Science 351, aad3000-1 (2016).
[2] L. M. Ghiringhelli et al., Phys. Rev. Lett. 114, 105503 (2015).

Title : First-principles study of magnetism and phase stabilities of V2 based antiferromagnetic Heusler semiconductors

Speaker : Fumiaki Kuroda

Abstract:

Antiferromagnetic materials have attracted much attention in the field of spintronics because of wide applications to exchange bias in magnetic tunnel junction and giant magneto-resistance devices, and spin- orbit transfer torque and anisotropic magnetoresistance in magnetic random access memory. Although several antiferromagnetic Heusler alloys have been examined for such applications, a drawback of the alloys is relatively lower transition temperatures than the ferromagnetic Heusler ones. D03 type V3Al that is iso-structural to the Heusler systems is known to be antiferromagnetic with high Neel temperature of 600 K, being a starting system for exploring candidates of antiferromagnetic Heusler alloys. In this work, we investigate the phase stability and magnetism of V2 based antiferromagnetic semiconductors by first- principles calculations. We first discuss the phase stability of the designed alloys by checking convex hull and found that keeping Al site is crucial to guarantee the stability against the segregation. In V2YAl (Y =Nb and Ta) systems, a relatively small hull distance was evaluated and the quite high Neel temperature higher than 1000K. The increase in the transition temperature from V3Al (NT=18) can be explained by considering the enhanced magnetic coupling between neighboring V atoms due to the expansion of lattice constant by doping larger 4d or 5d elements. By applying a uniaxial strain to induce tetragonal distortion and including the spin-orbit coupling, sizable magneto-crystalline anisotropy energy is obtained for V2YAl systems, implying that strained films can be used for antiferromagnetic spintronics.

Title : O2-Release and Structure Evolution of Li1.2M0.4Mf0.4O2 (M, Mf = Cr, Mn, Ti) Cathodes: First-Princips Calculations

Speaker : Motoyuki Hamaguchi

Abstract:

We have performed the first-principles calculations of Li1.2M0.4Mf0.4O2 (M, Mf = Cr, Mn, Ti) cathodes for Li-ion batteries to clarify microscopic reaction mechanisms including O2-release and structure evolution during charge and discharge reaction processes. We found that the O2-releases are suppressed in the Cr-systems, but the structure evolution with large volume changes is confirmed at low Li concentrations in the these systems.

Title : Summary of CrySPY

Speaker : Tomoki Yamashita

Abstract:

Development of efficient algorithms in crystal structure prediction is in great demand for data-driven material design. We have developed a tool for crystal structure prediction, CrySPY. I would like to summarize the current version of CrySPY.

Title : Conversion-Type Reaction Mechanism Analysis of Li-Ion Battery Cathode Material MF3 (M = Fe, Ti) by First-Principles Calculations

Speaker : Tatsuya Takahashi

Abstract:

Li-ion battery (LIB) is among the rechargeable batteries with high capacity, high voltage, and high cyclability, and used in many of mobile applications, vehicles, and natural power generations. Perovskite-type MF3 (M=Fe, Ti) are ones of the most promising cathodes for Li-ion batteries because of its much higher capacity than LiCoO2. However, their reaction mechanisms have not been completely revealed. In the previous works[1,2], x-ray absorption spectroscopy (XAS) spectra at the Fe K edge and its voltage profile during discharge-charge cycles were measured for compounds appearing in the reactions. From these measurements, the ionic valences of M change as +3, +2, and 0.For FeF3 system, the reaction path during the discharge process is presumed with the change of crystal structures along the increase of Li concentration, which is firstly the insertion reaction between the interatomic gaps of FeF3, and secondly the conversion reaction to two phases: Fe and LiF[2]. For TiF3 system, however, no more information of structural changes of cathode is not obtained from previous researches other than transition of ionic valence on Ti atom. In this study, we calculate, for both FeF3 and TiF3 systems, formation energy to evaluate the phase stability during the discharge process, voltage profile to check the reproduciblity of calculation to experiments, and density-of-states to estimate the ionic valence of Fe and Ti atoms. In this talk, I would like to discuss the comparison between FeF3 and TiF3 battery reaction.

[1] A. Kitajou, I. Tanaka, Y. Tanaka, E. Kobayashi, H. Setoyama, T. Okajima, S. Okada, Electrochemistry 85, 472 (2017).
[2] L. Li, R. Jacobs, P. Gao, L. Gan, F. Wang, D. Morgan, S. Jin, J. Am. Chem. Soc. 138, 2838 (2016).

Title : A study on spin Hall effect

Speaker : Vu Thi Ngoc Huyen

Abstract:

Spin Hall effect (SHE) was firstly proposed in a non-magnetic material more than forty years ago [1,2]. Observation of SHE in magnetic structure and ferromagnetic-nonmagnetic bilayer leads to the emergence of applicability in spintronic such as transistors or memory devices. There are two essential advantages of such devices. At first, it has a much faster switching time because of faster spin manipulation than charge. Secondly, it has lower power consumption than conventional devices because the processes are happening at a lower energy cost. Following our studying of anomalous Hall effect [3], I aim to search for materials showing significant spin Hall effect (SHE) and reveal a mechanism to enhance the spin Hall current. The magnetic structure of the system, if present, has to be considered with spin Hall conductivity (SHC) tensor [4]. Therefore, the characteristic of SHC tensor will be discussed in detail in this talk. I also present the results of SHC in paramagnetic Pt, Nb, Ta, which were obtained using PAOFLOW[5]. The PAOFLOW package is written by python 2.7, and it is useful to analysis materials properties including SHE, magnetic and spin circular dichroism, topology invariants, and so on.
[1] Dyakonov and Perel, Phys. Lett. 35A, 459 (1971)
[2] J. Sinova et al, Rev. Mod. Phys. 87, 1213 (2015)
[3] V. T. N. Huyen, M.-T. Suzuki, K. Yamauchi, T. Oguchi, Phys. Rev. B 100, 094426 (2019).
[4] M. B. Nardelli et al., Comput. Mater. Sci. 143, 462 (2018)
[5] M. Seemann et al., Phys. Rev. B 92, 155138 (2015)

Title : Analysis of structural stability of transition-metal compounds by using machine learning method

Speaker : Takafumi Hayashi

Abstract:

Recently, materials informatics (MI) has attracted much attention. MI is the field that utilize machine learning for materials science. It is used to predict physical properties of unknown materials, or to determine dominant variables of properties. Our aim is to understand dominant factors of structural and mechanical properties of MB, MC, and MN (M : 3d, 4d, and 5d transition-metals) by using the technique of MI. These transition-metal compounds are candidates for hard materials which are used for cutting tools, wear resistance parts and so on. Data about physical properties of transition-metal compounds can be obtained by the first-principles calculations[1]. We have focused on the structural stability of transition-metal compounds. We performed linear regression analysis of the total energy difference between two crystal structures. The linearly independent descriptor generation (LIDG) method is used for descriptors generation. By using LIDG method, we can get a high performance model. And then we performed descriptors selection to obtain a simple model with less number of descriptors. In this talk, I would like to talk and discuss about our regression analysis.

[1] M. Fukuichi, H. Momida, M. Geshi, M. Michiuchi, K. Sogabe, and T. Oguchi, J. Phys. Soc. Jpn. 87, 044602 (2018).

Title : Report of My Lectures at Juelich and Magnetic Symmetry Analysis of Band Splitting

Speaker : Hiroshi KATSUMOTO

Abstract:

I stayed in Forschungszentrum Juelich GmbH, Germany in October and I gave a intensive course consisting of four lectures on group representation theory in solid state physics. I also discussed about my recent research with some researchers. The lecture was based on a good text book to get start[1]. The lecture was consisted by four part. The first part is about the structure of a finite group and second, I explained the most important orthogonality theorems of matrix representation and character. At third, we exercised in deducing the character tables and projection operator and selection rule were shown. Finally, we reached to the representation of space group. I will report how the lectures was and the life in Juelich. In the second half of the colloquium, I would like to discuss the band structure in antiferromagnetic material, BiCoO3. The Rashba-type spin splitting in BiCoO3 was reported by DFT calculation[2]. Rashba effect is measured in nonmagnetic materials with strong spin-orbit coupling. The symmetry analysis of the Rashba effect that appears on the surface has already been made by using kp perturbation method[3]. Just as conventional space group symmetry and band structure are discussed, the band structure of materials with magnetism must also reflect that symmetry. In paramagnetic phase, the symmetry of a materials can be considered as double point group or double space group. Below Neel temperature, magnetic order realize and the symmetry of the material is lowering to magnetic space group from the original double group. I would like to introduce the structure of magnetic space group and apply the symmetry analysis to antiferromagnetic BiCoO3.
[1] M. Dresselhaus, G. Dresselhaus, and A. Jorio, Group Theory Application to the Physics of Condensed Matter, Cambridge: Springer. (2008)
[2] K. Yamauchi et al., arXiv:1910.06758[cond-mat] (2019).
[3] T. Oguchi and T. shishidou, J. Phys.: Condens. Matter 21, 092001 (2009).

Title : Anisotropic property of magnetic dipole in bulk, surface, and overlayer systems.

Speaker : Ryuta Matsumiya

Abstract:

The magnetic dipole is negligible in the Sz sum rule of XMCD, for ferromagnetic 3d transition-metal bulk systems, such as cubic Fe and Ni, and hcp Co.However, it can not be ignored in low dimensional systems such as films, multilayers, nano-wires and so on, so it is necessary to estimate the magnetic dipole as well[1]. Although using magnetic field induced by electric current to change the direction of magnetization is common, its energy consumption is not negligible due to Joule heating. Electric field induced magnetic anisotropy change is attracting the attention to solve such problem. his is called voltage-controlled magnetic anisotropy (VCMA). They try to reveal the microscopic origins of the VCMA in 3d ferromagnetic metals. Using in situ x-ray fluorescence spectroscopy that provides a high quantum efficiency, electric-eld-induced changes in orbital magnetic moment and magnetic dipole terms in ultrathin Co films are demonstrated. An orbital magnetic moment difference of 0.013muB was generated in the presence of electric fields of +-0.2V/nm. The VCMA of Co was properly estimated by the induced change in orbital magnetic moment, according to the perturbation theory model. The induced change in the magnetic dipole term only slightly contributed to the VCMA in 3d-ferromagnetic metals. Recent research has shown the significance of the magnetic dipole term in 5d state to the VCMA in Pt with proximity induced spin polarization[2].

[1] T. oguchi and T. Shishidou, Phys. Rev. B 70, 024412 (2004)
[2] T. kawabe et al, Phys. Rev. B 96, 220412(R) (2017)

Title : Battery Performance and Reaction Mechanism in Tin compounds as Negative Electrode: First-Principles Calculation

Speaker :

Abstract:

In recent years, the effective use of power generation systems using natural energy has been promoted due to increasing interest in environmental energy problems. In order to properly operate renewable energy power supply, a temporary storage of generated energy is effective. The construction of an large-scaled energy storage facility requires a secondary battery that excels in both cost and performance. In this study, we focus our attention on Sn compounds as candidate materials for negative electrodes. In Sn-compound negative electrodes, it is expected that two-types of battery reactions including conversion reactions and alloying reactions of Sn with Na can proceed sequentially and improve longevity of cycle characteristics of anodes. We calculate a phase diagram of ternary systems from formation energy, and clarify a possible reaction route considering intermediate products in discharge reactions. We calculate the voltage-capacity curves based on the reaction path obtained from the ternary phase diagram. To evaluate the battery performance, we compare the storage performance of Li and Na ion.

Title : Giant magnetocaloric effect with magnetostructural coupling of MnCoGe based alloy: First-principles calculation and Monte Carlo simulation

Speaker : Tran Ba Hung

Abstract:

Magnetocaloric effect is an intrinsic property of the magnetic material, the temperature and entropy of magnetic material is changed in adiabatic and isothermal process. This effect is promising for future cooling system. However, the isothermal entropy change of ordinary magnetocaloric material is usually not so high due to second order phase transition in magnetic part. The magnetostructural coupling gives the possible way to enhance the efficiency of the magnetocaloric effect due to the first order phase transition in both structure and magnetic of material [1]. In this work, we propose new model to reproduce the giant isothermal magnetic entropy change of experimental work of MnCoGe based alloys [2].
[1] J. Liu et al. Nature Materials 11, 620 (2012)
[2] S.K. Pal et al. Journal of Alloys and Compounds 775, 22 (2019)

Title : Electric-Field Control of 2D Magnetism in Bilayer VI3

Speaker : Thao Nguyen

Abstract:

At first part of my presentation, I would like to talk a bit about my trip to Italy last month. At second part, I would like to present my recent work on VI3, a new discovered material that belongs to the transition-metal trihalides 2D materials. While its structure and bulk properties have been investigated, there is a lack of information about the magnetism in the thin film. In this presentation, I will present my first-principles study on the magnetic properties in bilayer VI3 and the influence of applied electric-fields on the magnetism. I predict that the magnetic stability of bilayer VI3 systems can be tuned by external electric fields and the effect is comparable with the case of bilayer CrI3. To understand the physics behind, the geometry, stability, and electronic and magnetic properties of bilayer VI3 will be discussed by presenting the projected density of state and the band structure.

Title : Estimating the size of the supercell by calculating the Ni point defect in diamond.

Speaker : FUJIMURA Takkou

Abstract:

Since diamond is the hardest material, it is used as a cutting or polishing tool. Impurities in diamond are known to affect hardness and toughness. However, the detailed effects of impurities are not well understood. In the synthesis of diamond, 3d transition metals such as Ni and Co are often used as catalysts. Defects related to Ni in diamond are known, but complex defects and agglomeration mechanism of Ni are not well understood. Currently, we are calculating 3d transition metal impurities in diamond using the supercell method. First, the size of the supercell was obtained by calculating the Ni point defect at the substitutional site. I will talk about this.

Title : Introduction of XAS, XMCD, and RIXS

Speaker : Kazuki Ito

Abstract:

X-ray absorption spectroscopy (XAS) is a technique used to determine the electronic state and local structure of matter. X-ray absorption is measured by matching the incident light to the energy that can excite the inner shell electrons (approximately in the range of 0.1-100 keV). XAS is a type of absorption spectroscopy whose behavior follows quantum mechanical selection rules. X-ray magnetic circular dichroism (XMCD) is the difference spectrum between XAS measured in two magnetic fields, left and right circularly polarized. By analyzing the XMCD spectrum, we can understand the magnetic properties such as the spin and orbital magnetic moment of the atom. In the case of iron, the L-shell is usually used for the XMCD absorption spectrum. By absorbing X-rays of about 700eV, 2p electrons are excited and transition to 3d orbitals. Since the 3d state reflects the magnetic properties of the element, the spectrum contains information about the magnetic properties. This time, as a test calculation, the XMCD of iron was calculated by the first-principle calculation. Resonant inelastic X-ray scattering (RIXS) is a phenomenon in which X-rays enter a material and the inner shell electrons are resonantly excited into the outer shell state, and the excited state emits X-rays with energy smaller than the incident light and relaxes.

Title : Generation of descriptors of bulk modulus by LIDG

Speaker : Tanaka Yuki

Abstract:

Hard metals(eg: tungsten carbide, titanium carbide ), which are used for cutting tools, wear tools and so on, play an important role in manufacturing industries. However, there is concern about tight supply due to increasing demand.Transition-metal compounds are the alternative candidates. As the first step toward construction of the high performance model, I generated descriptors of bulk modulus of transition-metal compounds by linearly independent descriptor generation method. In my talk, I would like to talk about generated descriptors and the rough model of bulk modulus of transition-metal compounds.

Title :

Speaker : Shimazu Ryoma

Abstract:

The electronic ground state of a periodic system is usually described in terms of extended Bloch orbitals, but an alternative representation in terms of localized gWannier functionsh was introduced by Gregory Wannier. Then, methods have been developed that allow one to iteratively transform the extended Bloch orbitals of a first-principles calculation into a unique set of maximally localized Wannier functions.[1] First, Ifd like to talk about Bloch's theorem and talk about the conversion from it to the Wannier function. Then, talk about the edge band structure of the stanene, which is a 2D topological insulator, calculated using wannier90[2] and WannierTools[3] from the density of states by VASP.
[1]A.K. Geim, K.S. Novoselov, Nat. Mater., 183, 6 (2007)
[2]A. A. Mostofi, J. R. Yates, G. Pizzi, Y.-S. Lee, I. Souza, D. Vanderbilt and N. Marzari, Comput. Phys. Commun. 185, 2309 (2014)
[3] QuanSheng Wu, ShengNan Zhang, Hai-Feng Song, Matthias Troyer, Alexey A. Soluyanov, Comput. Phys. Commun. 224,405 (2018)

Title : Luong Huu Duc

Speaker :

Abstract:

P2 orthorhombic NaxMnO2 recently has been attractive to apply for cathode of rechargeable batteries. However, the diffusion mechanism of charge carriers inside this material has not been investigated clearly. In my presentation, I indicate the geometrical effect and small polaron migration on diffusion of charge carrier. My calculation shows that the migration of hole polaron formed in Na vacancy structure lower the diffusion since hole polaron migrates simultaneously with Na vacancy. The overall activation energy in full discharging process is 370 meV. In contrast, in the discharging process, the insertion of Na atom to MnO2 does not cause the polaron formation due to the inactive Jahn Teller Mn4+ ion. Without the small polaron formation, the activation energy decrease sharply to 90meV, benefit the Na ion diffusion.

Title : Development of program code for the first-principles photoemission-spectrum calculation

Abstract:

We are developing a program code for calculating a valence-band photoemission spectrum. As the first stage of the development, we employ a simple method in which the photoemission differential cross section of crystal is estimated by the sum of the product of the atomic-orbital photoionization differential cross section and the partial density of states of crystal. In this talk, the calculated spectrum of hard x-ray photoemission (HX-PES) is compared with the experiment for CuCrO$_2$ with the delafossite structure. The band structure calculation is done in the ferromagnetic (FM) state by using the FLAPW method in the local density approximation (LDA). The photoemission spectrum is calculated as the sum of atomic-orbital contributions. The photon-polarization dependence is reproduced fairly well. The horizontal' (theta = degree) spectrum mainly consists of emissionfrom Cu 4s, Cu 3d, and Cr 4s states, while the s-state contributions disappear in the vertical' (theta = 90 degree) spectrum, where theta is the angle between the photon-polarization direction andthe emitted photoelectron direction.

Title : Reconsidering of fermi surface of USi3

Speaker : kota watanabe

Abstract:

We are studing for new superconductor; UTe2. LDA calculations show that this material is insulator. But in the real, this is a metal. The interaction of 5f electrons make difficult this calculation but other factor maybe exists. I focus on USi3 to search problem in LDA. The interaction of 5f electrons in USi3 is weak. So LDA is good approximaton. But the size of fermi surface of 6d electrons in USi3 isn't calculated correctly. So I will search problem of LDA in calculation for USi3. If I could get the method to require this proalem, I will use the method for UTe2.

Title : Fracture mechanics of hard materials by first-principles calculations

Speaker : Hiroyoshi Momida

Abstract:

We have investigated mechanical properties including elastic and fracture behaviors of hard materials. Using the first-principles calculations, we have performed tensile test simulations of diamond and tungsten carbide to evaluate theoretical stress-strain curves. Effects of defects in the materials on the fracture behaviors are discussed.

Title : Looking back 2019

Speaker : Kunihiko Yamauchi

Abstract:

In this talk, I will briefly introduce my recent paper [1]. If time permits, I will show some photos and look back what I experienced this year.
[1] KY, P. Barone, and S. Picozzi, "Bulk Rashba effect in multiferroics: A theoretical prediction for BiCoO3", Phys. Rev. B 100, 245115 (2019).

Title : Stabilities of hydrogenated La(Fe_0.88 Si_0.12)_13 (La-Fe-Si) alloys at their Curie temperatures.

Speaker : Yukihiro Makino

Abstract:

Experiments showed the unstabilities of hydrogenated La-Fe-Si alloys at their Curie temperatures. The alloys decomposed into a fraction with an increased Curie temperature and another with decreased Curie temperature.[1, 2] I calculated the mixing energies of hydrated La-Fe-Si with Akai-KKR, and which showed unstable properties.
[1] IEEE TRANSACTIONS ON MAGNETICS, 47, 3391 (2011).
[2] J. Alloys Compd. 485, 313 (2009).

Title : EELS Spectra of Graphene Edges

Speaker : Tamio Oguchi

Abstract:

The electron energy loss spectroscopy (EELS) especially for high-energy loss is described with electron excitation processes essentially equivalent to those in the x-ray absorption spectrocopy (XAS). Thus, the EELS double differential scattering cross section obserbed is a good correspondece to the XAS transition probability within a certain approximation. Recently, several edge structures in graphene have been investigated by an atom-by-atom probe based on the EELS. [1] In this study, model systems are constructed for the edge structures in grapehne and their EELS spectra calculated from first principles with the explicit existence of core hole are compared with the experiment and discussed in terms of core-hole screening distinctive of the local structure.
1. K. Suenaga, M. Koshino, Nature 468, 1088 (2010).

Title : Theoretical investigation of p-type thermoelectric Mg2Si

Speaker : Naomi Hirayama

Abstract:

We have theoretically investigated the structural and electronic properties of impurity-doped magnesium silicide (Mg2Si) using first-principles calculations. Mg2Si, a narrow gap semiconductor, is a promising candidate for mid-temperature thermoelectric applications. In the present study, the hole doping of Mg2Si with various impurity atoms has been investigated. As a result, the most acceptors exhibit comparable formation energies for different impurity sites (Mg, Si, and interstitial ones), which may explain the experimental instability of their p-type conductivity. Furthermore, the interstitial insertion of Cl and F atoms into the crystal lattice leads to hole doping because of their high electronegativity.

Title : Ga-vacancy-enhanced ferromagnetism in Eu-doped GaN

Speaker : Akira Masago

Abstract:

Eu-doped GaN is a luminescent and ferromagnetic material, and this is a promising material for spintronics. It is computationally demonstrated that room-temperature ferromagnetism, which has been experimentally observed, is induced by holes in N 2p states (i.e., Zener's double exchange interaction) that arise from Ga vacancies as a result of the introduction of Eu ions (i.e., volume compensation). In this presentation, I would like to consider how to use this phenomena to spintronics materials.

Title :

Speaker : Hitoshi Fujii

Abstract:

Title :

Speaker : Koun Shirai

Abstract: