Phonon dispersion curves show how phonon energy depends on the q-vector, along high symmetry directions in the Brillouin zone. This information can be obtained experimentally from neutron scattering experiments on single crystals. Such experimental data are available for only a small number of materials and thus, theoretical dispersion curves are useful for both establishing the validity of a modeling approach and to demonstrate the predictive power of ab initio calculations.
In certain circumstances it is possible to measure the density of states (DOS) rather than the phonon dispersion. Furthermore, the electron-phonon interaction function, which is directly related to the phonon DOS can be measured directly in the tunneling experiments (see, for example, Yanson, 1988). It is therefore important to be able to calculate phonon DOS from first principles, in order to compare the results with experimentally observed spectra.
Materials Studio can produce phonon dispersion and DOS charts from any
.phonon CASTEP output file.
These files are hidden in the Project Explorer but a
.phonon file is generated with every
.castep file that has a
PhonDisp or PhonDOS suffix. All the files that can be used in the analysis of the current calculation will be presented in the
results file selector.
However, it is not recommended that you create phonon DOS plots based on the results of a phonon dispersion calculation that only uses q-vectors
in high-symmetry directions.
When evaluating phonon DOS, use only the results of the phonon calculations on the Monkhorst-Pack grid.
To create a phonon dispersion chart
seedname Phonon Dispersion.xcd, is created in the results folder.
To create a phonon DOS chart
seedname DOS.xcd, is created in the results folder when Full density of states is selected. A document seedname PDOS.xcd, is created in the results folder when Partial density of states is selected.
Analyzing CASTEP results
Phonon dispersion selection - CASTEP Analysis dialog
Phonon density of states selection - CASTEP Analysis dialog
Results file selector