Constant pressure molecular dynamics for molecular systems

Technical aspects of the constant pressure molecular dynamics (MD) method proposed by Andersen and extended by Parrinello and Rahman to allow changes in the shape of the MD cell are discussed. The new MD method is extended to treat molecular systems and to include long range charge-charge interactions. Results on the conservation laws, the frequency of oscillation of the MD cell, and the equations which constrain the shape of the MD cell are also given. An additional constraint is introduced to stop the superfluous MD cell rotation which would otherwise complicate the analysis of crystal structures. The method is illustrated by examining the behaviour of solid nitrogen at high pressure.