Structural behavior of UO2 under high-pressure up to 300 GPa 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 38 GPa. It agrees well with experiment observed ∼42 GPa. A new iso-structural transition following that is also predicted taking place from 80 to 130 GPa, which has not yet been observed in experiments. Further high compression beyond 226 GPa will result in a metallic and paramagnetic transition. It corresponds to a volume of 90Å 3 per cell, in a good agreement with previous theoretical analysis in the reduction of volume required to delocalize 5f states.

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Theory of the condensed state D 1000 Data-Driven Atomic Environment Prediction for Binaries Using the Mendeleev Number. Part 1. Composition AB. -(VILLARS*, P.; CENZUAL, K.; DAAMS, J.; CHEN, Y.; IWATA, S.; J. Alloys Compd. 367 (2004) 1-2, 167-175; Mater. Phases Data Syst., CH-6354 Vitznau, Switz.; Eng.) -Schramke 23-004

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