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 allow four‐indexed quantities containing one or two indices in the virtual orbital space to be stored across the global memory of distributed‐memory parallel processors. Quantities such as the double‐excitation amplitudes can now be distributed over multiple nodes, with blocks of data 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 basis sets, the structure of each tautomer and the transition state connecting the two minima has been determined at the SCF level. The relative energy difference and the activation energy were then redetermined using the MP2, CCSD, and CCSD(T) methods. All calculations have been performed on Intel distributed‐memory supercomputers. The largest coupled‐cluster calculations contained over 2 million double‐excitation amplitudes. © John Wiley & Sons, Inc.