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Yoshida Lab Tatsuo Kano 1.  Introduction Computational Materials Design First-principles calculation DFT(Density Functional Theory) LDA(Local Density.

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Presentation on theme: "Yoshida Lab Tatsuo Kano 1.  Introduction Computational Materials Design First-principles calculation DFT(Density Functional Theory) LDA(Local Density."— Presentation transcript:

1 Yoshida Lab Tatsuo Kano 1

2  Introduction Computational Materials Design First-principles calculation DFT(Density Functional Theory) LDA(Local Density Approximation) SIC(Self Interaction Correction)  YBa 2 Cu 3 O 6+y Crystal structure Phase diagram  Summary  My work 2

3  Calculation & Simulation  Physical properties  New ideas  Experiments 3

4  Predict physical properties of materials ← Input parameters: Atomic Number and Atomic position  No external parameters (experimental values) required.  Advantage ・ Low costs ・ Extreme conditions ・ Ideal environment 4

5 v eff ( r ) ψi(r)ψi(r) ? 5

6 We do not know the v xc and we need approximate expressions of them to perform electronic structure calculations. For a realistic approximation, we refer homogeneous electron gas. When the electron density changes in the space, we assume that the change is moderate and the electron density is locally homogeneous. Local Density Approximation (LDA) 6

7  For almost of all materials, the LDA can describe electronic structures reasonably ! Calculated atomic volume (lattice constant) as a function of atomic number. 笠井英明,赤井久純,吉田博 編 ; 「計算機マテリアルデザイン」(大阪大学出 版会) O E total r (lattice constant) a E min 7

8 LDA(Local Density Approximation) error may occur magnetic and strongly-correlated systems. Underestimation of lattice constant. Overestimation of cohesion energy. Underestimation of band gap energy. Occupied localize states (d states) at too high energy. 8

9  LDA error can be attributed to the presence of the self-interaction (SI) in the LDA energy function.  The SI is present in systems characterized by spatially localized electron charges such as 2 p, 3 d, and 4f electrons.  SIC is a solution of the error. A. Filippetti, N. A. Spaldin, Phys. Rev. B67, (2003) 9

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11 Superconductivity Electrical resistance → 0 Meissner effect 1911 Hg (4.2K) 1986 La-Ba-Cu-O 1987 YBa 2 Cu 3 O 6+y (90K) J.G.Bednorz and K.A.Muller ; Z.Physik B64,189 (1986) La-Ba-Cu-O 11

12 YBa 2 Cu 3 O 6+y (simple tetragonal ) YBa 2 Cu 3 O 7 (simple orthorhombic ) Warren E. Pickett ; Rev. Mod. Phys. 61, 433 (1989) Cu O Ba Y 12

13 Eg(LDA)Eg(expt)M(LDA)M(expt) YBa 2 Cu 3 O eV1.7eV M. A. HOSSAIN et al. Nature Phys. 4, JULY (2008) y 0.51 P. Wei, Z. Qing ; Phys. Rev. B49, 17 (1994) 0 13

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15 My workMy work  I will calculate electronic properties of YBCO using the self-interaction correction method.  I will observe change of magnetism with doping. 15

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17 A. Filippetti, N.A. Spaldim ; Phys. Rev. B67, (2003) 17

18 M. A. HOSSAIN et al. Nature Phys. 4, JULY (2008) 18

19 a Å b Å c Å z Cu z O z O z O z Ba YBa 2 Cu 3 O 7 Warren E. Pickett ; Rev. Mod. Phys. 61, 433 (1989) (simple orthorhombic ) 19

20 Ferromagnetism( 強磁性) Antiferromagnetism( 反強磁 性) Paramagnetism (常磁性) 20

21 YBa 2 Cu 3 O 6+y (simple tetragonal ) YBa 2 Cu 3 O 7 (simple orthorhombic ) Warren E. Pickett ; Rev. Mod. Phys. 61, 433 (1989) 21

22 AF YBa 2 Cu 3 O 6 PM YBa 2 Cu 3 O 7 22

23 super-cell method 23

24 the doping hole forms a dispersed 1.5 eV wide band. a b the dispersion is strongly one-dimensional. 24

25 n( r ) → E 25

26 LDA(Local Density Approximation) error may occur magnetic and strongly-correlated systems. Underestimation of lattice constant. Overestimation of cohesion energy. Underestimation of band gap energy. Occupied localize states (d states) at too high energy. P. Wei, Z. Qing ; Phys. Rev. B49, 17 (1994) 26

27 wurtzite 27


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