The hybrid halide perovskite CH 3 NH 3 PbI 3 exhibits a complex structural behaviour, with successive transitions between orthorhombic, tetragonal and cubic polymorphs at ca. 165 K and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH 3 NH 3 PbI 3 . The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of the sample. Despite a clear separation in energy between low frequency modes associated with the inorganic (PbI -3 ) n network and high-frequency modes of the organic CH 3 NH + 3 cation, significant coupling between them is found, which emphasises the interplay between molecular orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI 6 octahedra around room temperature.

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First-principles lattice-dynamics calculations are used to model and compare the vibrational spectra and thermal transport of four bulk tin-sulphide materials.

In the past two decades the public sector has experienced a transformation. A major feature of this change has been the displacement of the old style public administration by a “new public management” which focuses on results and measurement and in which accounting has a central role. This study reports on a survey of accountants in the public sector to determine the extent to which the changing public sector is accompanied by changes in accounting practices and to explore the process by which such changes are effected.