Revealing the Effect of Irradiation on Cement Hydrates: Evidence of a Topological Self-Organization

Despite the crucial role of concrete in the construction of nuclear power plants, the effects of radiation exposure (i.e., in the form of neutrons) on the calcium–silicate–hydrate (C–S–H, i.e., the glue of concrete) remain largely unknown. Using molecular dynamics simulations, we systematically investigate the effects of irradiation on the structure of C–S–H across a range of compositions. Expectedly, although C–S–H is more resistant to irradiation than typical crystalline silicates, such as quartz, we observe that radiation exposure affects C–S–H’s structural order, silicate mean chain length, and the amount of molecular water that is present in the atomic network. By topological analysis, we show that these “structural effects” arise from a self-organization of the atomic network of C–S–H upon irradiation. This topological self-organization is driven by the (initial) presence of atomic eigenstress in the C–S–H network and is facilitated by the presence of water in the network. Overall, we show that C–S–H exhibits an optimal resistance to radiation damage when its atomic network is isostatic (at Ca/Si = 1.5). Such an improved understanding of the response of C–S–H to irradiation can pave the way to the design of durable concrete for radiation applications

High-Performance Scalable Molecular Dynamics Simulations of a Polarizable Force Field Based on Classical Drude Oscillators in NAMD

Incorporating the influence of induced polarization in large-scale atomistic molecular dynamics (MD) simulations is a critical challenge in the progress toward computations of increased accuracy. One computationally efficient treatment is based on the classical Drude oscillator in which an auxiliary charged particle is attached by a spring to each nucleus. Here, we report the first implementation of this model in the program NAMD. An extended Lagrangian dynamics with a dual-Langevin thermostat scheme applied to the Drude−nucleus pairs is employed to efficiently generate classical dynamic propagation near the self-consistent field limit. Large-scale MD simulations based on the Drude polarizable force field scale very well on massively distributed supercomputing platforms, the computational demand increasing by only a factor of 1.2 to 1.8 compared to nonpolarizable models. As an illustration, a large-scale 150 mM NaCl aqueous salt solution is simulated, and the calculated ionic conductivity is shown to be in excellent agreement with experiment