Quantitative approach to the off-center model in CuCl

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Abstract
We use a model potential which includes the Madelung and van der Waals attraction and the Born-Mayer-Verwey repulsion to obtain a quantitative estimate of the vibrational and structural properties of CuCl at different temperatures and hydrostatic pressures. To achieve this goal we gather and use all relevant experimental data including our new temperature-dependent phonon-polariton measurements. We obtain a double-well potential which is able to reproduce the vibrational anomalies as observed by Raman scattering, infrared, and phonon-polariton measurements. The structural implications of the model are discussed and compared with extended x-ray absorption fine-structure and x-ray- and neutron-diffraction results. Our approach is valid also for the other Cu halides as well as for AgI for which data less extensive than those available for CuCl can be found.