Parallel coupled-cluster algorithm

A. P. Rendell, M. F. Guest, and R. A. Kendall,/. Comput. Chem., 14, 1429 (1993). Distributed Data Parallel Coupled Cluster Algorithm Application to the 2-Hydroxypyridine/2-Pyridone Tautomerism. 

Kobayashi, R., and A. P. Rendell. A direct coupled cluster algorithm for massively parallel computers. Chem. Phys. Lett. 265 1-11,1997. 

Our multipole code D-PMTA, the Distributed Parallel Multipole Tree Algorithm, is a message passing code which runs both on workstation clusters and on tightly coupled machines such as the Cray T3D/T3E [11]. Figure 3 shows the parallel performance of D-PMTA on a moderately large simulation on the Cray T3E the scalability is not affected by adding the macroscopic option. 

This becomes more complicated once the algorithm is parallelized to utilize modem computer architectures. Again one may therefore consider to utilize existing implementations of coupled cluster techniques to benefit from the work done in this area. The first step would be to derive a restricted algorithm that can be compared to non-relativistic closed shell algorithms. 

In multiple walkers metadynamics there is no efficiency gain in computing time, as the same accuracy could be obtained by performing just a single simulation Nj, -times longer. However, because the walkers are weakly coupled, this algorithm can be run easily on a parallel machine or even on a weakly inter-coimected cluster. Only a shared file system is required to allow interwalker commuitication in typical implementations. Moreover, it is not even necessary to start all the walkers at the same time, and there is no practical problem if one or more of the simulations is interrupted at some point. 

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