Interatomic-potential dependence and quenching-rate effects on the structure and mechanical anisotropy of amorphous tobermorite

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Abstract
The effects of different interatomic potentials on the amorphous structure of 1.1 nm tobermorite, a representative structural model for calcium–silicate–hydrate (C–S–H), are investigated systematically by molecular dynamics simulations using empirical potential Clayff, density functional theory (DFT), and machine-learning interatomic potential (MLMD) (Allegro-FM). Amorphous structures obtained through DFT and Allegro-FM are in agreement with each other when quenched from the same molten structure. In contrast, the structure generated using Clayff differs significantly from those obtained using these two approaches. The analysis of the radial distribution functions reveals that, except for the Si–O interaction, all interatomic distances obtained with Clayff are longer than those predicted by DFT and Allegro-FM. Consequently, the amorphous structure obtained with Clayff exhibits a lower density than those of the other two models. In addition to static structural analysis, the tensile response of amorphous tobermorite prepared at different quenching rates is examined using the MLMD Allegro-FM, and tensile simulations are performed along the x-, y -, and z -directions. The resulting stress–strain curves exhibit a clear dependence on the quenching rate (708, 70.8, and 7.08 K ps −1 ). Mechanical anisotropy gradually diminishes with a decreasing quenching rate. This finding demonstrates that even subtle variations in the static structure significantly influence dynamic behavior, and that isotropic mechanical responses emerge when a sufficiently slow quenching is employed, i.e. the elastic anisotropy becomes negligible when the cooling duration is further increased.
Funding Information
  • JST SPRING, Japan (JPMJSP2162)
  • JSPS KAKENHI (24K07630)

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