Distributing the Intramolecular Bonded Terms

DL_POLY_2 handles the intramolecular in which the atoms involved in any given bond term are explicitly listed. Distribution of the forces calculations is accomplished by the following scheme:

1. Every atom in the simulated system is assigned a unique index number from $1$ to $N$;
2. Every intramolecular bonded term $U_{type}$ in the system has a unique index number $i_{type}$: from $1$ to $N_{type}$ where $type$ represents a bond, angle or dihedral.
3. A pointer array $key_{type}(n_{type},i_{type})$ carries the indices of the specific atoms involved in the potential term labelled $i_{type}$. The dimension $n_{type}$ will be $2,~3$ or $4$, if the term represents a bond, angle or dihedral.
4. The array $key_{type}(n_{type},i_{type})$ is used to identify the atoms in a bonded term and the appropriate form of interaction and thus to calculate the energy and forces. Each processor is assigned the independent task of evaluating a block of ( $Int(N_{total}/N_{nodes})$) interactions.

The same scheme works for all types of bonded interactions. The global summation of the force arrays does not occur until all the force contributions, including nonbonded forces has been completed.