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This study demonstrates and tests the refinement of a lattice-dynamical model derived from periodic ab initio calculations at the Γ point against elastic diffraction data (X-ray or neutron). Refinement of only a handful of parameters is sufficient to obtain a similar agreement with the data as the conventional crystallographic model using anisotropic displacement parameters. By refinement against X-ray data, H displacement parameters are obtained which compare favourably with those from neutron diffraction experiments. The approach opens the door for evaluating thermodynamic properties, and for refinement against multi-temperature data, against inelastic diffraction data, spectroscopic information and thermal diffuse scattering data.

Supporting information

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Portable Document Format (PDF) file https://doi.org/10.1107/S2053273315024699/ae5006sup1.pdf
Additional statistics for the refinements, final refined parameters of the normal-mode refinement, and a figure showing the residual density of urea after refinement using NoMoRe and IAM refinement in SHELXL

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Zip compressed file https://doi.org/10.1107/S2053273315024699/ae5006sup2.zip
CIF files containing the refined models of urea

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Zip compressed file https://doi.org/10.1107/S2053273315024699/ae5006sup3.zip
Output files from the Crystal09 program, giving detailed information about the normal-mode coordinates of the refined models

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Portable Network Graphics (PNG) image https://doi.org/10.1107/S2053273315024699/ae5006sup4.png
Figure for use in JMol showing the normal modes of urea


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