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

Abstract

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 p1/2 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 calculationmore » 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.« less

Authors:

Sadigh, Babak; Kutepov, Andrey; Landa, Alexander; Söderlind, Per

Publication Date:

2019-11-21

Research Org.:

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

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

OSTI Identifier:

1579488

Alternate Identifier(s):

OSTI ID: 1578244

Report Number(s):

LLNL-JRNL-787823; BNL-212394-2019-JAAM
Journal ID: ISSN 2076-3417; ASPCC7; 983245

Grant/Contract Number:  

AC52-07NA27344; SC0012704

Resource Type:

Accepted Manuscript

Journal Name:

Applied Sciences

Additional Journal Information:

Journal Volume: 9; Journal Issue: 23; Journal ID: ISSN 2076-3417

Publisher:

MDPI

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; density functional theory; actinide elements; spin-orbit interaction; electron correlation