  Melting of uranium dioxide (UO2) nanocrystals has been studied by molecular
dynamics (MD) simulation. Ten recent and widely used sets of pair potentials
were assessed in the rigid ion approximation. Both isolated (in vacuum) and
periodic boundary conditions (PBC) were explored. Using barostat under PBC the
pressure dependences of melting point were obtained. These curves intersected
zero near -20 GPa, saturated near 25 GPa and increased nonlinearly in between.
Using simulation of surface under isolated boundary conditions (IBC)
recommended melting temperature and density jump were successfully reproduced.
However, the heat of fusion is still underestimated. These melting
characteristics were calculated for nanocrystals of cubic shape in the range of
768-49 152 particles (volume range of 10-1000 nm^3). The obtained reciprocal
size dependences decreased nonlinearly. Linear and parabolic extrapolations to
macroscopic values are considered. The parabolic one is found to be better
suited for analysis of the data on temperature and heat of melting.
