Rigorous modelling of INS from first principles

- 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

Scattering Law

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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.

a-CLIMAX example

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This is an example of an INS spectrum of MgH_{2} 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.

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