MASSIVE PARALLELISM: THE HARDWARE FOR COMPUTATIONAL CHEMISTRY? M.F. GUEST AND P. SHERWOOD Department for Computation and Information, CCLRC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, Cheshire, UK AND J.A. NICHOLS High Performance Computational Chemistry Group, Env ironmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, PO Box 999, Mail Stop Kl-90, Richland,' WA . 99352, USA 1. Introduction Computational chemistry covers a wide spectrum of activities ranging from quantum mechanical calculations of the electronic structure of molecules, to classical mechanical simulations of the dynamical properties of many- atom systems, to the mapping of both structure-activity relationships and reaction synthesis steps. Although chemical theory and insight play im- portant roles in this work, the prediction of physical observables is almost invariably bounded by the available computer capacity. The potential of massively parallel computers , with hundreds to thou- sands of processors (MPPs) , to significantly outpace conventional super- computers in both capacity and price-performance has long been recog- nised. While increases in raw computing power alone will greatly expand the range of problems that can be treated by theoretical chemistry meth- ods, it is now apparent that a significant investment in new algorithms is needed to fully exploit this potential. Merely porting presently avail- able software to these parallel computers does not provide the efficiency required, with many existing parallel applications showing a deterioration in performance as greater numbers of processors are used . New algorithms T. Ebisuzaki et al. (eds.), New Horizons of Computational Science © Springer Science+Business Media Dordrecht 2001