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Computed Properties

Phonon Software ver. 6.15 allows to calculate the following material properties:

  • Phonon dispersion relations (PDR) ω(k,j),
  • Existence of a soft mode, which indicates dynamical instability of the crystal, and the relaxation path to lower symmetry phase. In particular cases the soft mode could help to describe transition states, which determine the diffusion constant.
  • Coloured phonon dispersion relations, where the colour denotes phonon intensity found via predefined filters. A filter is a type of form factor and depends on polarization vectors.
  • Transverse optic (TO) and longitudinal optic (LO) phonon modes at Γ point. To all these modes an irreducible representations are assigned. The LO modes show mixed representations in most of the cases.
  • Animate vibrational motion of any phonon mode selected by mouse pointer.
  • A displacement pattern for any phonon mode.
  • A symmetry reduction caused by phonon mode belonging to commensurate wave vector and selected by mouse pointer.
  • Search for most intense phonon mode across many Brillouin zones, using definite filter.
  • Phonon density of states (DOS) g(ω).
  • Partial phonon density of states gμ,i(ω) for a specific atom μ moving along i-direction.
  • Thermodynamical functions: internal energy E, entropy S, free energy F, heat capacity at constant volume cv, as a function of temperature T.
  • Thermal mean square displacement tensor, or Debye-Waller factor as a function of temperature.
  • Space group of the low-symmetry structure caused by a condensation of a multidimensional phonon soft mode, or any other combination of phonon modes, for example such which may strongly be coupled to electronic states.
  • Intensity of the inelastic coherent neutron scattering of a given phonon branch, and in selected Brillouin zone.
  • Spectra of the inelastic incoherent neutron scattering for monocrystal and polycrystal.
  • Intensity of the inelastic x-rays scattering of a given phonon branch, and in selected Brillouin zone.
  • Spectra of the inelastic nuclear scattering for monocrystal.
  • Phononic part of the dielectric tensor.
  • Vectors of mode effective charges for any direction of the unit vector of the wavevector in vicinity Γ point.
  • Frequencies of irreducible representations of TO and LO modes at Γ point. In particular, the LO mode frequencies depends on the directions the wavevector points at Γ.
  • Intensity of the infrared absorption spectra including LO/TO splittings.
  • Intensity of the Raman scattering spectra including LO/TO splittings (where relevant- in non-centrosymmetric crystals).

Procedures in which Phonon Software must be used many times:

  • Grüneissen parameters. Phonon frequencies should be calculated as a function of pressure.
  • Quasiharmonic approximation. Phonon frequencies should be calculated as a function of negative and positive pressures. Quasiharmonic approach relies on finding the scaling relation between pressure (calculated in ab initio runs), and temperature (found from a construction of thermodynamical behaviour of the free energy). In this way pressure dependence of a quantity is rescaled to temperature dependence. Thermal expansion and temperature-pressure phase diagram can be determined.
  • Detection of electron-phonon coupling. In these case electronic states must be calculated for such supercell for which atoms are displaced according to a frozen phonon.
  • Equilibrium parameters of chemical reaction with solid component. Free energy of the solid component contains phonon contribution.

Systems to be treated in Phonon Software:

  • Crystals classified by 230 crystallographic space groups.
  • Surfaces, multilayers, and interfaces within the slab method, if possible, using a crystallographic space group.
  • Crystals with point defects. The space group must be modified in order to account for the presence of defect.

Last update: July 20, 2014