Density-functional theory (DFT) is a powerful tool for predicting the stability of nuclear waste forms. However, many waste forms are metastable and synthesized at high temperatures. Therefore, the 0K nature of DFT calculations can potentially incorrectly predict the stability of synthesized waste forms with respect to competing products. Adding vibrational effects via phonon calculations can improve prediction accuracy but may not be practical for the typical crystal sizes. The Debye method approximates thermal affects via a cell volume and energy relationship, which is orders of magnitudes cheaper to compute than harmonic and quasi-harmonic phonon calculations. This study benchmarks the Debye approximation against harmonic and quasi-harmonic calculations for several small actinide oxides and salts as well as synthesized actinide salt inclusion complexes, demonstrating the methods effectiveness.

Benchmarking thermal approximations for actinide compounds

ACS Fall 2021

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