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.

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, central to the design of high-performance Si3N4 ceramics, has been sought for many years. Here we show direct images of dopant atoms (La) within the nanometre-scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La for the crystalline surfaces, which is essential for forming elongated grains and a toughened microstructure. Whereas principles of micrometre-scale structural design are currently used to improve the mechanical properties of ceramics, this work represents a step towards the atomic-level structural engineering required for the next generation of ceramics.

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The catalytic properties of transition metal particles often depend crucially on their chemical environment, but so far, little is known about how the effects of the environment vary with particle size, especially for clusters consisting of only a few atoms. To gain insight into this topic, we have studied the oxygen affinity of free Pt(x) clusters as a function of cluster size (x = 1, 2, 3, 4, 5, and 10) using density functional theory (DFT) calculations (GGA-PW91). DFT-based Nosé-Hoover molecular dynamics has been used to explore the configuration space of the Pt(x)O(x) and Pt(x)O(2x) clusters, leading to the discovery of several novel Pt-oxide structures. The formation of small Pt-oxide clusters by oxidizing the corresponding Pt(x) clusters is found to be significantly more exothermic than the formation of bulk Pt-oxides from Pt metal. The exothermicity generally increases as cluster size decreases but exhibits strongly nonlinear dependence on the cluster size. The nanoclusters are also structurally distinct from the bulk oxides and prefer one- and two-dimensional chain and ringlike shapes. These findings help elucidate the oxidation behavior of Pt nanoclusters and lay the foundation for understanding the reactivity of Pt nanoclusters in oxidizing chemical environments.