Assessing Relativistic Effects and Electron Correlation in the Actinide Metals Th to Pu

Journal Article · 21 November 2019 · Applied Sciences

DOI: https://doi.org/10.3390/app9235020 · OSTI ID:1579488

Sadigh, Babak ^[1]; Kutepov, Andrey  ^[2]; Landa, Alexander ^[1]; Söderlind, Per ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Brookhaven National Lab. (BNL), Upton, NY (United States)

Density functional theory (DFT) calculations are employed to explore and assess the effects of the relativistic spin–orbit interaction and electron correlations in the actinide elements. Specifically, we address electron correlations in terms of an intra-atomic Coulomb interaction with a Hubbard U parameter (DFT + U). Contrary to recent beliefs, we show that for the ground-state properties of the light actinide elements Th to Pu, the DFT + U makes its best predictions for U = 0. Actually, our modeling suggests that the most popular DFT + U formulation leads to the wrong ground-state phase for plutonium. Instead, extending DFT and the generalized gradient approximation (GGA) with orbital–orbital interaction (orbital polarization; OP) is the most accurate approach. We believe the confusion in the literature on the subject mostly originates from incorrectly accounting for the spin–orbit (SO) interaction for the p_1/2 state, which is not treated in any of the widely used pseudopotential plane-wave codes. Here, we show that for the actinides it suffices to simply discard the SO coupling for the p states for excellent accuracy. We thus describe a formalism within the projector-augmented-wave (PAW) scheme that allows for spin–orbit coupling, orbital polarization, and non-collinear magnetism, while retaining an efficient calculation of Hellmann–Feynman forces. We present results of the ground-state phases of all the light actinide metals (Th to Pu). Furthermore, we conclude that the contribution from OP is generally small, but substantial in plutonium.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC52-07NA27344; SC0012704
• OSTI ID: 1579488
• Report Number(s): BNL--212394-2019-JAAM; LLNL-JRNL--792557
• Journal Information: Applied Sciences, Journal Name: Applied Sciences Journal Issue: 23 Vol. 9; ISSN ASPCC7; ISSN 2076-3417
• Publisher: MDPICopyright Statement
• Country of Publication: United States
• Language: English