HYDROXYLATION-INDUCED SURFACE STABILITY OF ANO2 (AN = U, NP, PU) FROM FIRST-PRINCIPLES
The adsorption of dissociated water has a dramatic effect on the relative stability of the surfaces. Dissociated water, at one monolayer coverage, is adsorbed preferentially onto the (100) surface for all three AnO2 systems. In the case of UO2, for instance, the water adsorption energy on the (100) surface (-1.34 J/m2) is almost four times higher than the adsorption energy on the (111) surface (-0.35 J/m2), and almost twice as large as the adsorption energy on the (110) surface (-0.77 J/m2). Similar trend in the adsorption energies is observed for both NpO2 and PuO2. The calculated hydroxylated surface energies indicate that with a single monolayer coverage of H2O the (100) surface is more stable than either the (111) or the (110) surfaces. Consequently, the morphology of hydroxylated AnO2 crystallites will be no longer dominated by the (111), but rather the (100) facets.