I will present recent work concerned with two aspects of modeling materials behavior: one is related to fracture and the laws governing how that occurs and the other is related to how we may begin to simulate thousands of atoms starting with quantum mechanics. In the first topic, a new model is outlined for understanding the separation of surfaces that undergo relaxation or reconstruction upon formation of a crack. This is relevant for stress corrosion cracking, which happens on long time scales where the crack speed is slow compared to the time required for surface relaxation. We revisit the so-called Universal Binding Energy Relation (UBER), discussing the limits where it succeeds and where it fails, as well as why it fails, and then present a model that builds on UBER that can properly account for surface relaxation and reconstruction. In the second topic, we revisit an orbital-free version of density functional theory (DFT), which results in a linear scaling algorithm even for metals. This version of DFT requires not only the usual approximate functional of the density to represent quantum mechanical electron exchange and correlation, but also an approximate functional of the kinetic energy in terms of the density, as well as use of so-called local pseudopotentials to represent the nuclei+core electron interaction with the valence electrons. Progress made on both fronts, as well as outstanding issues, will be described.
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