Topic: defects in solids, metal-ion storage materials, hydrogen storage materials

Download these files. Be prepared: SIMAN package is needed (see here)

Practice

• Point defects in Li [recitationCD/*]
  • Determine equilibrium lattice parameter of bcc Li using conventional cubic cell with two atoms [Li2.full_relax].
  • Create 3x3x3 supercell of Li and calculate total energy [Li333.opt]. Compare energies per atom with primitive cell. Why they are slightly different?
  • Create vacancy, calculate total energy. Optimize the structure and calculate relaxation energy [Li333vac.opt]. Calculate vacancy formation energy and compare it with relaxation energy.
  • Add self-interstitial atom into tetrahedral and octahedral voids [InterstitialBCC.jpg]. Relax the structure, calculate total energy and formation energies [Li333tet.opt, Li333oct.opt]. Explain why formation energies are different. Compare relaxation energies of vacancy and self-interstitial.
  • Go to 4x4x4 or even 5x5x5 supercell to check the influence of supercell size on the formation energy of interstitial defects.
  • Estimate equilibrium concentrations of vacancies and self-interstitials at room temperature.
  • Create 3x1x1 supercell of Li with (100) surface. Why do we need to increase the cell size only in [100] direction?
  • Vary the thickness of vacuum layer from 1 to 10 A and for each case optimize the atomic positions and calculate total energies [Li_suf_i.opt]. Calculate surface energies (in J/m2) and plot them against vacuum thickness [gamma.png]. Determine the optimal vacuum thickness.
  • Compare calculated formation energies of defects with that in literature [literature/*].
• F-center in NaCl
• Dopants in Si

Reading

• C Freysoldt, B Grabowski, T Hickel, J Neugebauer, G Kresse, A Janotti, C G Van de Walle, First-principles calculations for point defects in solids, RMP 86, 253 (2014) – e