This work was supported by funds from the Environmental and Molecular Sciences Laboratory Construction Project at Pacific Northwest National Laboratory. Development of some of the parallel programming tools and algorithms employed by NWChem was performed under the auspices of the High Performance Computing and Communications Program of the Mathematical, Information, and Computational Sciences Division, U.S. Department of Energy. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830.