Numerical simulation of alpha-quartz under non-hydrostatic compression.   Memory glass and five-coordinated crystalline phases
  The behavior of $\alpha$-quartz under hydrostatic and non-hydrostatic high-pressure conditions has been investigated in Molecular Dynamics simulations of silica in order to clarify the role of non-hydrostatic stresses in the amorphization process. It is shown that the amorphization threshold is not modified if the stress along the {\bf c} direction is lowered, so that the mean amorphization pressure can effectively be lowered under non-hydrostatic conditions. On the other hand, the application of a positive uniaxial stress along the {\bf c} axis, results in the appearance of a new crystalline phase, where all silicon atoms are in five-fold coordination. 
James Badro, Jean-Louis Barrat, Philippe Gillet