Hugoniot constraint molecular dynamics study of a transformation to a metastable phase in shocked silicon

A molecular dynamics constraint based on the Hugoniot is formulated for the study of shocked materials. The constraint allows the simulation of a small part of the system under shock conditions for longer time periods than the use of a moving piston which creates a shock wave in a large system. It also allows for the use of quantum mechanical methods for which the work scales rapidly with system size. The constraint is used as a first approximation to study dynamical effects in shocked silicon. Transformations through metastable states are found under some conditions for shocks in the [111] direction using a tight-binding model. A new six-fold coordinated phase of silicon is found to be metastable under hydrostatic conditions using density functional theory.