Conclusion and outlook

The task-farming framework introduced into ChemShell has resulted in a substantial increase in the scalability of the code for the types of calculation considered. All three benchmarked cases (finite-difference Hessian, parallel nudged elastic band, and stochastic search) showed performance gains in excess of the targets set in the dCSE work program. All the programming objectives have therefore been achieved.

The main aim of future work will be to use the task-farming approach on HECToR for scientific applications. An ongoing collaboration with Prof. Catlow's group at UCL will use task-farmed calculations for the study of heterogeneous catalysis, with systems similar to the QM/MM test cluster that was used to benchmark the parallel NEB method. The task-farmed approach will also be useful in other areas where large-scale calculations are required, such as biomolecular modelling.

There are also still opportunities for further technical developments. First, the task-farming method could be extended to other types of chemical calculation, such as multiple trajectory calculations in molecular dynamics. We also plan to parallelise the finite-difference Hessian code in DL-FIND, which is used by several optimisation algorithms (this is equivalent to the force command in ChemShell and will benefit in the same way). Second, further modifications to GAMESS-UK could be made to allow alternative parallelisation methods (ScaLAPACK, global arrays) to work in the task-farmed environment. This is expected to be more technically challenging than the minor modifications required for PeIGS. Third, other codes could be modified to accept the MPI_COMM_WORKGROUP communicator and so work in task-farmed mode. The internal DL_POLY code in ChemShell is an obvious first candidate for this work, but collaborations with the developers of other external software packages is also a possibility.

The task-farming implementation will be made generally available as part of ChemShell version 3.4, which is scheduled for release in July 2010. Until then the pre-release code is available on request.

The work detailed in this report will be submitted for publication to Proceedings of the Royal Society A as part of a special issue on the activities of the Materials Chemistry Consortium.