DISTRIBUTED DATA-PARALLEL COUPLED-CLUSTER ALGORITHM - APPLICATION TO THE 2-HYDROXYPYRIDINE 2-PYRIDONE TAUTOMERISM

The recently developed parallel coupled-cluster algorithm of Rendell, Lee, and Lindh [Chem. Phys. Lett., 194, 84 (1992)] is extended to allo w four-indexed quantities containing one or two indices in the virtual orbital space to be stored across the global memory of distributed-me mory parallel processors. Quantities such as the double-excitation amp litudes can now be distributed over multiple nodes, with blocks of dat a retrieved from remote nodes by the use of interrupt handlers. As an application of the new code, we have investigated the potential energy surface of the 2-hydroxypyridine/2-pyridone tautomers. Using large ba sis sets, the structure of each tautomer and the transition state conn ecting the two minima has been determined at the SCF level. The relati ve energy difference and the activation energy were then redetermined using the MP2, CCSD, and CCSD(T) methods. All calculations have been p erformed on Intel distributed-memory supercomputers. The largest coupl ed-cluster calculations contained over 2 million double-excitation amp litudes. (C) 1993 by John Wiley & Sons, Inc.