In multiscale modeling of large-strain deformations, atomistic simulations of stress-induced structural instability in solids can lead to insights into various defect nucleation processes. In nano-indentation, discrete displacement bursts are shown to be homogeneous dislocation nucleation events rationalized by a site-specific stiffness criterion. In affine shear, electronic-structure calculations show that redistribution of charge densities during deformation governs the ideal shear strength of metals. Additionally molecular dynamics results reveal a 4-stage wave distortion scenario in the localization of a deformation twin. The advancement of sharp crack front under critical loading is elucidated by determining the saddle-point configuration using reaction pathway sampling. With this experience we have begun to model a unit process of water-silica reaction in which a single water molecule hydrolyzes the siloxane bond, a first step toward problems that combine chemistry and mechanics.
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