- It uses the isolated molecule approach for the study of molecular solids.
- For extended solid calculations the approximation is not longer necessary since there is no distinction between external and internal modes.
Calculation of INS spectra, the Scattering Law
Calculation of INS spectra using CASTEP
The normal modes are calculated for a large grid of points in the reciprocal space. In this example, the lattice was sampled as a 32x32x48 grid (the symmetry of the system makes that number smaller).
The INS spectra is generated from the eigenvectors and eigenvalues on every point in the grid.
This is an example of an INS spectrum of MgH2 calculated using CASTEP (full phonon calculation using the interpolation algorithm) and a-CLIMAX.
Ramirez-Cuesta, A. J. aCLIMAX 4.0.1, The new version of the software for analyzing and interpreting INS spectra. Computer Physics Communications 2004, 157 (3), 226-238.