List of Figures

2.1 Annotated example cell file for BN in the Wurtzite structure
2.2 Annotated example parameter file for BN in the Wurtzite structure
2.3 Output in the .castep file generated by the preceding input files. The columns show the mode frequencies, a letter labelling of the irreducible representation of the mode, the infrared absorptivity and raman activity, and whether or not the mode is raman and/or ir active. Not all of these are present in every calculation depending on the use of symmetry and input options. Note that the Γ point frequency table is repeated, excluding and including the non-analytic contribution which generates the LO/TO splitting in one or more directions (See Gonze and Lee [1]). The group theory analysis usually only corresponds to the full crystallographic point group in the case without symmetry breaking by LO/TO splitting.
2.4 Example cell file for aluminium supercell phonon calculation. This calculation computes a set of dispersion curves along high-symmetry directions. Note that this calculation is not fully converged with supercell size - there is a noticeable change in frequency on some of the branches on increasing the supercell matrix entries from 3 to 4.
2.5 Example param file for aluminium supercell phonon calculation. It is not strictly necessary to turn off the LO/TO splitting calculation - CASTEP will warn that this is not possible and turn it off anyway. The explicit request for a non-spin polarized calculation is necessary for fcc Al, because CASTEP chooses spin-polarized by default due to the odd number of electrons.
2.6 Extract from the .castep output file generated from the hexagonal BN run of figures 2.1, 2.2, with task : EFIELD. The Born effective charges are laid out with the columns representing the X,Y,Z electric field directions and the rows the X,Y,Z displacement directions.
3.1 Example output from based on the run of figure 2.3. Infrared spectrum and DOS curves based on just the TO modes or TO plus LO have been combined into into one plot with a slightly shifted baseline, scaled, and legends added.
3.2 Phonon dispersion curve plots of RbBr generated using the script and xmgrace. The Brillouin zone labelling is generated using the -symmetry fcc option. The left-hand plot was generated using the default branch crossing detection algorithm, which was disabled using the -nj option for the right-hand plot. The algorithm has discriminated between modes which do cross and the four genuine avoided crossings in the left-hand plot