Molecular dynamics simulation of UO2 nanocrystals surface

In this article we investigated surface of nanocrystals (NCs) of uranium dioxide (UO2) using molecular dynamics (MD) under isolated (non-periodic) boundary conditions in the approximation of rigid ions and pair potentials (RIPI). It is shown that a cubic shape of NCs is metastable and equilibrium is reached in the process of structural relaxation to the octahedral shape during long simulations of 1000 ns (200 million MD steps), which increase with the size of NC. We measured the size dependences of the lattice parameter and the surface energy density of cubic and octahedral NCs with volumes up to 1000 nm(3) (50000 particles) at temperatures of 2200 K and 2300 K. For the surfaces {1 0 0} and (1 1 1) we obtained the energy densities sigma(100) = 1.60 +/- 0.02 J/m(2), sigma(111) = 1.14 +/- 0.03 J/m(2) and surface tension constant gamma(111) = 0.841 +/- 0.008 J/m(2). The resulting ratio of sigma(100)/sigma(111) = 1.41 +/- 0.04 within the error coincides with the experimental value of 1.42 +/- 0.05 measured for microscopic cavities in UO2 monocrystals. (c) 2011 Elsevier B.V. All rights reserved.