Logo of Phonon

Phonon Software ver. 6.10. Last upgrade to ver. 6.15

Using the direct method the Phonon Software allows to calculate phonon dispersion curves, irreducible representation of modes (at Γ), phonon density of states, thermodynamic functions, Debey-Waller factors, inelastic neutron and x-rays scattering, dielectric constant, infrared absorption and Raman scattering. The input Hellmann-Feynman forces should be calculated by a standard ab initio software, like VASP, Wien2k, or others, which treat the considered crystal as a supercell. Due to crystal symmetry the HF forces should only be calculated for several displaced atoms in the supercell.

Phonon Software can also be used for modeling the lattice dynamics. This approach proves to be useful in order to obtain feeling on the phonon behaviour in a given material, since the force constants, and/or two-body spring constants have to be guessed by the User.

Phonon is designed to calculate lattice dynamics for crystals having one of 230 space groups, but calculations for surfaces and multilayers in slab approach, lattices with defects, etc. can also be done. All calculated results are written in a collection of text files, so that reuse, and/or replot of the data is available at any time.

Phonon Software, ver.6.15, is a further development of Phonon Software vers.4.28, 4.30, 5.10, 5.11, 5.12, 6.10, 6.11, 6.12, 6.13, 6.14 and 6.15.

The menu of Phonon Software ver. 6.15 contains the following options:

  • Files
    • New Project - initialization of a project either as Ab initio (Ai), or Modeling (Mo) phonons.
    • Open Project - activation of existing project.
    • Copy Project - copy active project to another one with a different name.
    • Delete Project - delete active project.
    • Import Model - download from a database a project ready to run. Structural parameters and Hellmann-Feynman file are included.
    • Preferences - shows license, and general option for Phonon Software appearance.
  • Create
    • Symmetry-Unit Cell - selection of the crystallographic space group of the project crystal, setting of lattice constants and angles. The 230 space groups are given in setting of either International Tables for Crystallography (1989), or in Kovalev (1965) setting (Ai,Mo).
    • Particles - construction of the crystal structure from non-equivalent positions of atoms (Ai,Mo). Constructed unit cells can be viewed. Introduction of effective charges tensors imported from (Ai) calculations can be symmetrized to satisfy requirement of crystal site symmetries.
    • Interaction Range - setting of supercell (Ai,Mo), or coordination shells (Mo) used later in derivation of the force constants for dynamical matrix. Possible automatic update of lattice constants and atomic positions after optimization by ab initio program (Ai). Any shape of supercell can be used. If the supercell breaks the crystal space group then the lower space group symmetry is accepted. Here are calculated the neighbor list, symmetry of force constants matrices and the numbers of independent force constant parameters (Ai,Mo). A set of displacements needed to calculate the Hellmann-Feynman forces for the direct method is proposed (Ai). A file with positions of all atoms of the supercell can be issued (Ai). The supercell can be viewed.
    • Hellmann-Feynman Forces (AI) - write here the HFFILE file of ab initio optimization: suppercell lattice constants, requirements to impose translational-rotational invariances, and name of Hellmann-Feynman file. At this option force constant matrices are derived from the supplied Hellmann-Feynman forces, collected in HFFILE, using direct method. If needed the force constants can be modified to fit additionally the phonon frequencies to experimental points. Plot of the value of the force constant elements as a function of distance demonstrates the decay of potential interaction with distance.
    • Potential Parameters (Ai,Mo) - a formulae to introduce the values of independent parameters of the force constants by hand. For some high-symmetry crystals Invariances option allow to impose on force constants the translational-rotational invariances.
    • Report - text file reporting results obtained while running options under Create (Ai,Mo).
  • Analyze
    • Dispersion Curves - first specify the wave vectors along which the phonon dispersion relations (PDR) will be calculated. Then, plot the PDR. The PDR can be also plotted using colours, where the colour is defined by the intensity involved in a phonon mode. The intensity is calculated with the aim of polarization vectors according to separately determined filters. With mouse a single component of phonon mode can be selected on the plot of PDR and the atomic vibrations in crystal supercell can be animated. Phonon Software has a build-in animator routine based on OpenGL. Similarly for single mode selected with the mouse the low symmetry space group appearing as a result of condensation of this mode, can be found by applying the FindSym program of H.T.Stokes and D.M.Hatch from Brigham Young University. Phonon software finds the irreducible representations for all phonon modes at the Brillouin zone center. Another option allows to search over many Brillouin zones to find the Brillouin zone of most intense phonon mode.
    • Mode Displacements - permits toelaborate arbitrary number of irreducible representations, including all the irreducible components and irreducible arms, to search for displacement pattern, symmetry reduction and animate several phonon modes simultaneously as specified in dialogs.
    • Density of States - determines an plots the phonon density of states (DOS) and partial phonon density of states for all atoms and all axes x, y, z calculated by Monte Carlo sampling of the Brillouin zone.
    • Thermodynamics - plots of internal energy, free energy, entropy, heat capacity at constant volume, all components of the the symmetric tensor of thermal mean square displacements as a function of temperature, and in harmonic approximation.
  • Spectroscopy
    • Neutron Scattering - using PDR and DOS, taking into account the corresponding neutron scattering cross-sections, the peak intensities of PDR for coherent neutron scattering, and incoherent inelastic scattering on polycrystals and monocrystals are calculated for any geometry. For incoherent scattering on polycrystals the multiphonon correction can be added.
    • X-rays Scattering - using PDR and DOS, taking into account the corresponding atomic form factors, the peak intensities of PDR for x-rays scattering, and nuclear inelastic scattering on monocrystals are calculated for any geometry. For nuclear inelastic scattering the multiphonon correction can be added.
    • Dielectric Properties - determines the dielectric tensor in phononic harmonic phonons. The mode effective charges for the Γ Brillouin zone point can be calculated for any unit vector pointing to Brillouin zone center. The complete group theoretical analysis of the transverse TO and longitudinal LO optic phonon modes is made.
    • Infrared Absorption - using Born effective charges for TO and LO modes for polarized and unpolarazed light, the IR spectra for monocrystal and polycrystal can be determined.
    • Raman scattering - are calculated using the Raman tensors. These tensors must be calculated within ab initio code (Ai) from changes of dielectric constant caused by a displacement of a single atom, one at a time. This approach resembles calculations of Hellmen-Feynman forces for deriving the phonon frequencies.
  • Help
    • Phonon Manual - provides detailed description of all of Phonon Software options.

Last update: July 20, 2014