Ab initio molecular dynamics study of the pressure-induced phase transformations in cristobalite - art. no. 104106

The mechanism for the pressure-induced transformation of cristobalite to st ishovite and post-stishovite phases has been obtained from constant pressur e ab initio molecular dynamics simulations. The cristobalite to stishovite transformation is found to be a two step process where SiO4 tetrahedra firs t rotate followed by a lattice distortion to yield the six-coordinated stis hovite structure. Further compression of stishovite yields the CaCl2 struct ure and is followed by another six-coordinated structure with symmetry P2(1 )/n (at 11 Mbars) which remains stable to a pressure of about 14 Mbars and then transforms into a nine-coordinated P2(1)/m structure.