Frozen Atoms

DL_POLY_2 also allows atoms to be completely immobilised (i.e. ``frozen'' at a fixed point in the MD cell). This is achieved by setting all forces and velocities associated with that atom to zero during each MD timestep. Frozen atoms are signalled by assigning an atom a non-zero value for the freeze parameter in the FIELD file. DL_POLY_2 does not calculate contributions to the virial or the stress tensor arising from the constraints required to freeze atomic positions. In DL_POLY_2 the frozen atom option cannot be used for sites in a rigid body. As with the tethering potential, the reference position is scaled with the cell vectors in constant pressure simulations.

In DL_POLY_2 the frozen atom option is handled by the subroutine FREEZE.