Research Interests
Computational simulations of solid materials behavior (alloys and oxide semiconductors), mostly based on First Principles calculations; Thermodynamic properties (stability and phase diagram) of alloys with Monte Carlo, CVM [cluster variation] and CEM [cluster expansion] methods; phase transitions of quantum systems; solid state physics under extremely conditions [High pressures and shock impacts] and (non-)equilibrium statistical mechanics.
Research result
The structural behavior of uranium dioxide under pressure up to 300 GPa was investigated by the DFT method with GGS and LSDA approximations plus (or not) Hubbard U correction for strong correlated on-site Coulomb interactions. Comparison with experiment showed that LSDA+U gives the best description for UO2 in the fluorite phase. However, the calculated transition pressure to the Pnma phase with the same U parameter was quite low, indicating that the value of U depends on structure or lattice distortions sensitively. A better value of U for the Pnma phase is obtained, which removes the factitious energy barrier predicted by U=4.5 eV. The error due to varying of U is estimated as just half of the error given by the GGS and LSDA approximations, showing that LSDA+U is more reliable. Higher pressure leads to an isostructural transition followed by a metallic-paramagnetic transition, which takes place between 226 and 294 GPa with an effective cubic lattice parameter as 82%–84% of the fluorite phase at zero pressure, in good agreement with previous theoretical analysis. [See full text]
Strong compositional effects on EOS of substitutional binary alloys, which shows various related quantities varying with concentration around stoichiometry with a surprising W-shape, such as the thermal expansion coefficient, the heat capacity, and the Gruneisen parameter. Click the figure to see details.
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