Abstract
The structure of diopside (CaMgSi2O6) has been calculated at pressures between 0 and 25 GPa using the planewaves and pseudopotentials approach to density functional theory. After applying a pressure correction of 4.66 GPa to allow for the under-binding usually associated with the generalized gradient approximation, cell parameters are in good agreement with experiment. Fitting to the third-order Birch–Murnaghan equation of state yields values of 122 GPa and 4.7 for the bulk modulus and its pressure derivative. In addition to cell parameters, our calculations provide all atomic positional parameters to pressures considerably beyond those currently available from experiment. We have analyzed these data in terms of polyhedral rigidity and regularity and find that the most compressible Ca polyhedron becomes markedly less anisotropic above 10 GPa.
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Acknowledgments
We thank NERC for funding under grants NE/C515698/1 and NE/C515704/1. AMW also gratefully acknowledges a NERC Postdoctoral Research Fellowship (NE/E012922/1) and thanks E. Palin for assistance in preparing the figures. The computational results in this paper were obtained using NW-GRID resources, a collaboration of Daresbury Laboratory and the Univerties of Lancaster, Liverpool and Manchester with funding from the North West Development Agency.
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Walker, A.M., Tyer, R.P., Bruin, R.P. et al. The compressibility and high pressure structure of diopside from first principles simulation. Phys Chem Minerals 35, 359–366 (2008). https://doi.org/10.1007/s00269-008-0229-3
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DOI: https://doi.org/10.1007/s00269-008-0229-3