Original Paper

Physics and Chemistry of Minerals

, Volume 35, Issue 7, pp 359-366

The compressibility and high pressure structure of diopside from first principles simulation

  • Andrew M. WalkerAffiliated withDepartment of Earth Sciences, University of Cambridge Email author 
  • , Richard P. TyerAffiliated withSTFC Daresbury Laboratory
  • , Richard P. BruinAffiliated withDepartment of Earth Sciences, University of Cambridge
  • , Martin T. DoveAffiliated withDepartment of Earth Sciences, University of Cambridge

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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.

Keywords

Diopside Density functional theory Equation of state Pyroxene Compression