The DL_POLY_2 RESPA Program is a variant of DL_POLY_2 that handles the time reversible, multiple timestep RESPA algorithm due to Tuckerman and Berne [19,20] as implemented by Procacci and Marchi for atomic and rigid ion systems[21]. However, it is not applicable to systems which have rigid body molecules or constraints, and for this reason the RESPA code is kept separate from the DL_POLY_2 main source in the sub-directory called respa.
The DL_POLY_2 implementation allows the user to define three concentric regions around a given atom. Forces deriving from atoms in the innermost region are updated more frequently (i.e. every timestep) than those in the immediate outer region, which in turn are updated more frequently than those deriving from the outermost region. This (depending on the relative sizes of each region and the frequency of the forces update) can represent a great computational saving. This is coupled with the advantage that the algorithm is time reversible and therefore possesses long term stability.
The method is fully documented in [21]. A makefile (Makefile_respa) is available in the build sub-directory, which will build the RESPA program (DLRESPA.X). A test case may be found in the data sub-directory.