Co-array Fortran (CAF) and Unified Parallel C (UPC) are two emerging languages for single-program, multiple-data global address space programming. These languages boost programmer productivity by providing shared variables for inter-process communication instead of message passing. How- ∗ This work was supported in part by the Department of Energy under Grant DE-FC03-01ER25504/A000, the Los Alamos Computer Science Institute (LACSI) through LANL contract number 03891-99-23 as part of the prime contract (W-7405-ENG-36) between the DOE and the Regents of the University of California, Texas Advanced Technology Pro- gram under Grant 003604-0059-2001, and Compaq Com- puter Corporation under a cooperative research agreement. The computations were performed in part on an Itanium cluster purchased with support from the NSF under Grant EIA-0216467, Intel and Hewlett Packard, and on the Na- tional Science Foundation Terascale Computing System at the Pittsburgh Supercomputing Center. This research was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user fa- cility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory. Pacific Northwest is operated for the Department of Energy by Battelle