The latest release of NWChem delivers an open-source computational chemistry package with extensive capabilities for large scale simulations of chemical and biological systems. Utilizing a common computational framework, diverse theoretical descriptions can be used to provide the best solution for a given scientific problem. Scalable parallel implementations and modular software design enable efficient utilization of current computational architectures. This paper provides an overview of NWChem focusing primarily on the core theoretical modules provided by the code and their parallel performance.

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The ground-state electronic structure of NiO and MnO has been calculated within the Hartree-Fock approximation using local Gaussian basis sets. For both, a qualitatively correct ground-state electronic structure is obtained in which the wide-band-gap insulating character of these materials is seen to be a result of large on-site Coulomb interactions. The materials are correctly predicted to be antiferromag- Recent experimental and theoretical evidence has led to the speculation that the upper valence band in these materials is primarily 0 2p in character. " This has important consequences regarding both the nature of hole states and the valency of the higher oxides, and has led to the suggested classification of NiO as a chargetransfer insulator. '