We have adapted classical molecular dynamics to study the structural and dynamical properties of amorphous silica surfaces. Concerning the structure, the density profile exhibits oscillations perpendicularly to the surface as observed in liquid metal surfaces and the pair correlation functions as well as the angle distributions show features (absent in the interior of the films) that can be attributed to the presence of 2-fold rings which are perpendicular to the surface. From the mean-squared displacement of the non bridging oxygen atoms we find that in the interior region they move perpendicular to the surface while they move parallel to it in the surface region.

In the context of studies on long-time storage of irradiated spent fuel, molecular dynamics simulations have been carried out in order to understand the physical phenomena, on the atomic scale, linked to modifications and damage that the uranium dioxide structure undergoes during a-decay irradiation in repository conditions. Simulations of atomic displacement cascades over an energy range from 1 to 20 keV for the initial primary knock-on atom (PKA) do not show any amorphization of the structure in agreement with what has been found experimentally, and there is very little correlation between the initial orientation of the PKA and the cascade morphology. The number of Frenkel pairs, as a function of the initial energy of the PKA, exhibits a power-law behaviour with an exponent of 0.9 which is contrary to the theoretical linear Norgett-Robinson-Torrens law. Finally, for both species the vacancies have a tendency to aggregate and cluster near the core of the cascade while interstitial atoms are preferentially located at the periphery of the branches corresponding to subcascades.

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