Density Functional Theory Study of the Structural Properties of PuH_x, 2<=x<=3

TL;DR

This study uses density functional theory with a Hubbard U correction to analyze the structural properties of plutonium hydrides PuH2 and PuH3, revealing how stacking and electronic correlations influence their energetics and hysteresis.

Contribution

It provides a detailed DFT-based analysis of PuH_x compounds, highlighting the importance of electronic correlations and stacking effects in their structural stability.

Findings

Agreement between DFT and experimental structures when including Hubbard U

Stacking of Pu planes influences the energy and hysteresis behavior

Interstitial H positions and magnetic structures have negligible energy impact

Abstract

Plutonium dihydride and trihydride show strikingly similar crystal structures when viewed as close-packed Pu planes with ABC and AB stacking, respectively. The similarity serves as a framework for density functional theory (DFT) calculations of PuH2, PuH3, and intermediate compositions. Agreement between structures observed in experiment and in the DFT description of the Pu-H system requires accounting for the strong electronic correlation in the f orbitals, achieved here with the addition of a Hubbard parameter U. The hysteresis measured between hydriding and dehydriding can be attributed to the effect of stacking of the close-packed Pu planes on the energy as a function of stoichiometry, calculated using the GGA+U approach. Changes in the interstitial positions occupied by the H atoms affect the energy by amounts that are negligible compared to room temperature; changes in the magnetic structure lead to equally small energy differences.