Barostats

The size and shape of the simulation cell may be dynamically adjusted by coupling the system to a barostat in order to obtain a desired average pressure ($P_{\rm ext}$) and/or isotropic stress tensor ( $\mbox{$\underline{\underline{\bf\sigma}}$}$). DL_POLY_2 has two such algorithms: a Hoover type barostat and the Berendsen barostat. Only the former has a well defined conserved quantity.