Ab initio study of MgSiO3 low-clinoenstatite at high pressure

Abstract We investigated the athermal high-pressure behavior of the structural properties of MgSiO3 low clinoenstatite using the plane wave pseudopotential method within the local density approximation. The experimental zero pressure structure and pressure variations of the lattice parameters were reasonably well reproduced. The calculated atomic positions vary slightly and monotonically with pressure. Our results showed that MgO6 octahedra are three times more compressible than SiO4 tetrahedra, consistent with the general observation that the SiO4 tetrahedra are nearly incompressible in silicates. Mg2O6 octahedra (the larger of two Mg sites) remain most distorted over the pressure regime studied while Mg1O6 octahedra and both types of SiO4 tetrahedra show similar level of distortions. The tetrahedral chain angles were shown to slightly vary with pressure indicating that the structure under compression always remains highly distorted away from the ideal close-packing of O atoms.

[1]  G. D. Price,et al.  Ab initio elasticity and thermal equation of state of MgSiO3 perovskite , 2001 .

[2]  Stefano de Gironcoli,et al.  Ab initio lattice dynamics of MgSiO3 perovskite at high pressure , 2000 .

[3]  B. Karki,et al.  Ab initio structure of MgSiO3 ilmenite at high pressure , 2000 .

[4]  Stefano de Gironcoli,et al.  First-principles determination of elastic anisotropy and wave velocities of MgO at lower mantle conditions , 1999, Science.

[5]  G. D. Price,et al.  Computer modelling of a pressure induced phase change in clinoenstatite pyroxenes , 1997 .

[6]  Hamann.  Generalized gradient theory for silica phase transitions. , 1996, Physical review letters.

[7]  G. D. Price,et al.  Ab initio study of MgSiO3 C2/c enstatite , 1995 .

[8]  R. Angel,et al.  Equations of state and thermodynamic properties of enstatite pyroxenes , 1994 .

[9]  Price,et al.  Ab initio molecular dynamics with variable cell shape: Application to MgSiO3. , 1993, Physical review letters.

[10]  Andrew Putnis,et al.  An Introduction to Mineral Sciences , 1992 .

[11]  R. Angel,et al.  Stability of high-density clinoenstatite at upper-mantle pressures , 1992, Nature.

[12]  G. D. Price,et al.  Computer simulation of the MgSiO3 polymorphs , 1992 .

[13]  Martins,et al.  Efficient pseudopotentials for plane-wave calculations. , 1991, Physical review. B, Condensed matter.

[14]  T. Gasparik,et al.  Reversals of the orthoenstatite‐clinoenstatite transition at high pressures and high temperatures , 1990 .

[15]  F. Birch,et al.  Equation of state and thermodynamic parameters of NaCl to 300 kbar in the high‐temperature domain , 1986 .

[16]  Y. Ohashi.  Polysynthetically-twinned structures of enstatite and wollastonite , 1984 .

[17]  R. Hazen,et al.  Comparative Crystal Chemistry: Temperature, Pressure, Composition and the Variation of Crystal Structure , 1982 .

[18]  A. Zunger,et al.  Self-interaction correction to density-functional approximations for many-electron systems , 1981 .

[19]  D. Chadi,et al.  Special points for Brillouin-zone integrations , 1977 .

[20]  G. V. Gibbs,et al.  Quadratic Elongation: A Quantitative Measure of Distortion in Coordination Polyhedra , 1971, Science.

[21]  N. Morimoto,et al.  The crystal structures of clinoenstatite and pigeonite , 1960 .

[22]  Stefano de Gironcoli,et al.  High-pressure lattice dynamics and thermoelasticity of MgO , 2000 .

[23]  D. T. Griffen.  Silicate Crystal Chemistry , 1992 .