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Simulations of TiO2(both rutile and anatase) nanoparticles with water, methanol, and formic acid were conducted using a ReaxFF reactive force field to investigate the characteristic behavior of reactivity to these organic solvents. The force field was validated by comparing water dissociative adsorption percentage and bond length between Na and O with density functional theory (DFT) and experimental results. In the simulations, 1-nm rutile and anatase nanoparticles with water, methanol, and formic acid were used, respectively. The numbers of attached hydroxyl with time and nanoparticles distortion levels are presented. We found that the rutile nanoparticle is more reactive than the anatase nanoparticle and that formic acid distorts nanoparticles more than water and methanol. [ABSTRACT FROM AUTHOR]

• ReaxFF force field parameters are newly developed for Ni-Cr-Fe-H-O system. • The driving forces for atomistic SCC initiation were calculated. • The classic slip-dissolution model for SCC initiation is extended. Targeting atomistic initiation of stress corrosion cracking (SCC) of Alloy 690, reactive molecular dynamics simulations of SCC of polycrystalline Ni 60 Cr 30 Fe 10 alloys under water with dissolved oxygen at 900 K were performed employing newly developed reactive force field (ReaxFF) of Ni-Cr-Fe-H-O system. Observed atomistic mechanochemical mechanism involve dissolution-precipitation and diffusion-oxidation behaviors for corrosion, and cleavage-slipping-twinning behaviors for cracking initiation with its driving forces including loacl shear stress/strain and oxidation-enhanced atomistic stress. Roles of cold work, tensile strain and grain boundary (GB) structures in impacting these mechanochemical behaviors were explored based on calculated surface and GB energy, GB diffusivity and atomistic stress/strain. [ABSTRACT FROM AUTHOR]

Quantifying the irreversible chemical and structural changes of Si during cycling remains challenging. In this study, a continuous reactive molecular dynamics delithiation algorithm, with well-controlled potential gradient and delithiation rate, was developed and used to investigate the "natural" delithiation responses of an aluminum-oxide coated silicon thin-film. Fast delithiation led to the formation of dense Si network near the surface and nanoporosity inside the a-LixSi, resulting in 141% volume dilation and significant amount of Li trapped inside (a-Li1.2Si) at the end of delithiation process. In contrast, slow delithiation allowed the a-LixSi to shrink by near-equilibrium condition, demonstrating no permanent inner pore with nearly Li-free structure (a-Li0.2Si) and minimal volume dilation (44%). However, even without trapped Li, the delithiated a-LixSi still exhibited higher volume (lower density) than the equilibrium structure with the same Li concentration, despite delithiation rate. The origin of this excess volume is the loss of directly bonded Si–Si pairs, which made the subsequent relithiation faster. On the basis of the atomistic modeling and the quantified degradation mechanism, battery operating guidelines, including the delithiation rate and the depth of charge to avoid trapped Li and coating delamination, were suggested to improve the durability Si electrodes. [ABSTRACT FROM AUTHOR]