Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.

The use of Hermite Gaussian auxiliary function densities from the variational fitting of the Coulomb potential for the calculation of exchange-correlation potentials is discussed. The basic working equations for the energy and gradient calculation are derived. The accuracy of this approximation for optimized structure parameters and bond energies are analyzed. It is shown that the quality of the approximation can be systematically improved by enlarging the auxiliary function set. Average errors of 0.5 kcal/mol are obtained with auxiliary function sets including f and g functions. The timings for a series of alkenes demonstrate a substantial performance improvement.

Studies involving small iron oxide cationic clusters, Fe m O n + (m = 1, 2, n = 1−5), and their reactivity in the presence of CO at near thermal energies were conducted by employing a guided ion beam mass spectrometer. Observed reaction channels included CO oxidation and oxygen replacement by CO which are shown to be dependent on cluster size and stoichiometry. First principles electronic structure studies within the density functional theory framework were carried out to address the structures and energetics of small cationic clusters and to probe the molecular level pathways for CO oxidation. The theoretical calculations, in conjunction with the experimental findings, are used to propose a coherent picture about the trends in the dissociation energies, which are largely dependent upon the metal to oxygen ratio, and the nature of the structure−reactivity relationships for the formation of the reaction products.

International audienceThis article provides a brief overview of the quantum chemical auxiliary density functional theory program deMon2k. A basic introduction into its key computational features is given. By selected examples, it is shown how deMon2k can contribute to the elucidation of problems in chemistry, biology, and materials science such as finite temperature effects, nuclear magnetic resonance studies, structure determinations, heterogeneous, and enzymatic catalysi