The structural behavior of UO2 under high pressure up to 300GPa has been studied by first-principles calculations with LSDA+U approximation. The results show that a pressure-induced structural transition to the cotunnite-type (orthorhombic Pnma) phase occurs at 38GPa. It agrees well with the experimentally observed ~42 GPa. An isostructural transition following that is also predicted to take place from 80 to 130GPa, which has not yet been observed in experiments. Further high compression beyond 226GPa will result in a metallic and paramagnetic transition. It corresponds to a volume of 90A^3 per cell, in good agreement with a previous theoretical analysis in the reduction of volume required to delocalize 5f states.
@article{arxiv.cond-mat/0703656,
title = {Structural behavior of uranium dioxide under pressure by LSDA+U calculations},
author = {H. Y. Geng and Y. Chen and Y. Kaneta and M. Kinoshita},
journal= {arXiv preprint arXiv:cond-mat/0703656},
year = {2007}
}