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Prof. Sanjay. V. Khare Department of Physics and Astronomy,

Ab initio calculations for properties of β-In 2 X 3 (X = O, S, Se, Te) and β-X 2 S 3 (X = Al, Ga, In). Prof. Sanjay. V. Khare Department of Physics and Astronomy, The University of Toledo, Toledo, OH-43606 http://www.physics.utoledo.edu/~khare/. Outline. Structural details

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Prof. Sanjay. V. Khare Department of Physics and Astronomy,

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  1. Ab initio calculations for properties of β-In2X3 (X = O, S, Se, Te) and β-X2S3(X = Al, Ga, In) Prof.Sanjay. V. Khare Department of Physics and Astronomy, The University of Toledo, Toledo, OH-43606 http://www.physics.utoledo.edu/~khare/

  2. Outline • Structural details • Length Scales and Techniques • Ab initio method • Various properties of β-In2X3 (X = O, S, Se, Te) and β-X2S3 (X = Al, Ga, In) • DOS and LDOS plot of β-In2X3 (X = O, S, Se, Te) and β-X2S3 (X = Al, Ga, In)

  3. Band structures of β-In2X3 (X = O, S, Se, Te) • and β-X2S3 (X = Al, Ga, In)

  4. Structural details β-In2X3 (X = O, S, Se, Te) and β-X2S3 (X = Al, Ga, In) all belong to same space group and there details are as follows • Pearson Symbol: tI80 • Space Group: I41/amd • Number: 141

  5. Theoretical Techniques and Length Scales • 10 – 100 nm and above: Continuum equations, FEM simulations, numerically solve PDEs, empirical relations. • 1-10 nm: Monte Carlo Simulations, Molecular Dynamics, empirical potentials.   • < 1 nm Ab initio theory, fully quantum mechanical. • Integrate appropriate and most important science from lower to higher scale.

  6. Value of ab initio method • Powerful predictive tool to calculate properties of materials • Fully first principles ==> • (1) no fitting parameters, use only fundamental constants (e, h, me, c) as input • (2) Fully quantum mechanical for electrons • Thousands of materials properties calculated to date • Used by biochemists, drug designers, geologists, materials scientists, and even astrophysicists! • Evolved into different varieties for ease of applications • Awarded chemistry Nobel Prize to W. Kohn and H. Pople 1998

  7. What is it good for? • Pros • Very good at predicting structural properties: • (1) Lattice constant good to 1-10% • (2) Bulk modulus good to 1-10% • (3) Very robust relative energy ordering between structures • (4) Good pressure induced phase changes • Good band structures, electronic properties • Good phonon spectra • Good chemical reaction and bonding pathways • Cons • Computationally intensive, band gap is wrong • Excited electronic states difficult

  8. Various properties of β-In2X3 (X = O, S, Se, Te)

  9. DOS and LDOS plots for β-In2X3(X = O, S, Se, Te)

  10. Brillouin zone for tetragonal structure Band structures of β-In2O3 Eg = 0.6 eV (direct band gap)

  11. Brillouin zone for tetragonal structure Band structures of β-In2S3 Eg = 1.02 eV (indirect band gap)

  12. Brillouin zone for tetragonal structure Band structures of β-In2Se3 Eg = 0.23 eV (indirect band gap)

  13. Brillouin zone for tetragonal structure Band structures of β-In2Te3 No band gap

  14. Internal Parameters

  15. Internal Parameters

  16. Various properties of β-X2S3 (X = Al, Ga, In)

  17. DOS and LDOS plots for β-X2S3(X = Al, Ga, In)

  18. Brillouin zone for tetragonal structure Band structures of β-Al2S3 Eg = 1.48 eV (indirect band gap)

  19. Brillouin zone for tetragonal structure Band structures of β-Ga2S3 Eg = 0.9 eV (indirect band gap)

  20. Brillouin zone for tetragonal structure Band structures of β-In2S3 Eg = 1.02 eV (indirect band gap)

  21. Internal Parameters

  22. Internal Parameters

  23. Collaborators Institutional Support • Prof. S. Marsillac. • (Department of Physics and Astronomy, The University of Toledo, Toledo, OH-43606.) • N. S. Mangale. • (Department of Electrical Engineering and Computer Science, The University of Toledo, Toledo, OH-43606.) • Photovoltaic Innovation and Commercialization Center (PVIC) • Ohio Supercomputer Cluster • National Center for Supercomputing Applications (NCSA)

  24. Thank You

  25. Evolution of theoretical techniques • The physical properties of any material are found to be related to the total energy or difference between total energies. • Total energy calculation methods which required specification of number of ions in the material are referred to as ab initio methods. • Ab initio make use of fundamental properties of material. No fitting parameters are involved.

  26. Ab initio techniques and approximations • Techniques: • Density functional theory • Pseudopotential theory • Iterative diagonalization method • Approximations: • Local density approximation • Generalized gradient approximation • Different codes like SIESTA, VASP, CASTEP are used. • VASP - Vienna Ab initio Simulation Package Graph showing the comparison of wave function and ionic potential in Pseudopotential theory.

  27. Details of our ab initio method • LDA, Ceperley-Alder exchange-correlation functional as parameterized by Perdew and Zunger • Used the VASP code with generalized ultra-soft Vanderbilt pseudo-potentials and plane wave basis set • Supercell approach with periodic boundary conditions in all three dimensions • Forces converged till < 0.01 eV/ Å • Used supercomputers of NCSA and OSC

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