High-precision molecular dynamics simulation of UO2-PuO2: superionic transition in uranium dioxide

TL;DR

This study uses high-precision molecular dynamics simulations with GPU acceleration to analyze the superionic phase transition in uranium dioxide, providing detailed insights into the transition's temperature and pressure dependence.

Contribution

It evaluates the accuracy of the top 10 interatomic potentials in reproducing the superionic transition in UO2 using high-precision simulations.

Findings

Reliable detection of superionic transition with 1K accuracy.

Pressure dependence of the transition characterized, showing parabolic amplitude and linear temperature change.

Smoother and wider {bb}-peaks than previously assumed.

Abstract

Our series of articles is devoted to high-precision molecular dynamics simulation of mixed actinide-oxide (MOX) fuel in the rigid ions approximation using high-performance graphics processors (GPU). In this article we assess the 10 most relevant interatomic sets of pair potential (SPP) by reproduction of the Bredig superionic phase transition (anion sublattice premelting) in uranium dioxide. The measurements carried out in a wide temperature range from 300K up to melting point with 1K accuracy allowed reliable detection of this phase transition with each SPP. The {\lambda}-peaks obtained are smoother and wider than it was assumed previously. In addition, for the first time a pressure dependence of the {\lambda}-peak characteristics was measured, in a range from -5 GPa to 5 GPa its amplitudes had parabolic plot and temperatures had linear (that is similar to the Clausius-Clapeyron equation for melting temperature).