Abstract
AbstractComputer simulations are routinely performed to model the response of materials to extreme environments, such as neutron (or ion) irradiation. The latter involves high-energy collisions from which a recoiling atom creates a so-called atomic displacement cascade. These cascades involve coordinated motion of atoms in the form of supersonic shockwaves. These shockwaves are characterized by local atomic pressures >15 GPa and interatomic distances <2 Å. Similar pressures and interatomic distances are observed in other extreme environment, including short-pulse laser ablation, high-impact ballistic collisions and diamond anvil cells. Displacement cascade simulations using four different force fields, with initial kinetic energies ranging from 1 to 40 keV, show that there is a direct relationship between these high-pressure states and stable defect production. An important shortcoming in the modeling of interatomic interactions at these short distances, which in turn determines final defect production, is brought to light.
Highlights
As scientific computing becomes evermore ubiquitous, it is common practice to simulate the effect of extreme environments on materials using molecular dynamics (MD)
The evolution of high-energy displacement cascades can pressures as high as 50 GPa in 10 keV cascades. Such pressures are conveniently be subdivided into three distinct phases: a comparable to those observed during short-pulse laser ablation, supersonic phase, a sonic phase and a thermally enhanced high-energy impacts and diamond anvil cells
Current modeling techniques are probably adequate to identify general features of these high-energy phenomena, our analysis indicates that the force fields used to compute short-range interactions require more physically based constraints to generate quantitatively accurate simulation results
Summary
As scientific computing becomes evermore ubiquitous, it is common practice to simulate the effect of extreme environments on materials using molecular dynamics (MD). The supersonic wave leaves behind a region of high atomic volume and small or negative local pressure In this cross-section, one can identify two interacting shockwaves. The atoms displaced by the sonic wave recover their original positions During this phase, temperatures can be very high in the core of the cascade (reaching over 4,500 K in the low-density pockets of our 10 keV simulations); atoms that were displaced during the supersonic phase remain very mobile and many recombine with vacant lattice sites. It is possible to predict, on average, how many stable defects number of final stable defects created by the PKA in the Ni will be present in the system by measuring the number of atoms crystal At this stage of cascade development, the local material state is described by the least accurate part of classical force fields.
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