We investigated the athermal high-pressure behavior of the structural prope
rties of MgSiO3 low clinoenstatite using the plane wave pseudopotential met
hod 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 monoton
ically with pressure. Our results showed that MgO6 octahedra are three time
s more compressible than SiO4 tetrahedra, consistent with the general obser
vation that the SiO4 tetrahedra are nearly incompressible in silicates. Mg2
O6 octahedra (the larger of two Mg sites) remain most distorted over the pr
essure regime studied while MglO(6) octahedra and both types of SiO4 tetrah
edra show similar level of distortions. The tetrahedral chain angles were s
hown to slightly vary with pressure indicating that the structure under com
pression always remains highly distorted away from the ideal close-packing
of O atoms.