Influence of point defects and impurities on the dynamical stability of<i>δ</i>-plutonium

Dorado, Boris; Bieder, Jordan; Torrent, Marc

doi:10.1088/1361-648x/aa6eb7

Cited by 7 publications

(6 citation statements)

References 69 publications

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“…For example, in δ plutonium, the local density approximation (LDA) or GGA approximations of DFT leads to a dynamically unstable phase. However, using DFT used with orbital polarization (DFT+OP) [9], or DFT+U [39], or DFT+DMFT [12], a dynamically stable phase is obtained, even at 0 K. This seems in agreement with experimental spectra [40], which are however measured in a PuGa alloy, in which the δ phase is stabilized at room temper ature. However, in pure plutonium, the δ phase is stable only above ≃700 K. Thus, at room temperature or below, no exper imental conclusion can be drawn on the dynamical stability of the δ phase of pure plutonium because there is no exper imental measurement of phonon spectra.…”

Section: Introductionsupporting

confidence: 75%

“…Indeed, we showed in [28] that spin-orbit coupling is necessary for a good description of structural properties and that the cRPA effective Coulomb interaction is ≃1 eV. However, [39,41] neglects spin-orbit coupling, and use a large value of U, [9,39,41] use a local magnetic moment in contradiction to experiment [2] and [12] uses a large value of U.…”

Section: Introductionmentioning

confidence: 88%

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A unified and efficient theory for the structural properties of actinides and phases of plutonium

Amadon

Dorado

2018

J. Phys.: Condens. Matter

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We show that a calculation using density functional theory (DFT) in the generalized gradient approximation (GGA) supplemented by an explicit Coulomb interaction term between correlated electrons (GGA+U), can accurately describe structural properties of (1) the room temperature phases of U, Np, Pu, Am and Cm, and (2) the α, β, γ, δ and ϵ phases of plutonium, as does the combination of GGA with dynamical mean field theory (DMFT). It thus changes the view on the role of electronic interaction in these systems and opens the way to fast calculations of structural properties in actinides metallic system. We use ab initio values of effective Coulomb interactions and underline that Hund's exchange and spin-orbit coupling are of utmost importance in these calculations. Secondly, we show that phonons properties in δ plutonium are impacted by strong interactions. The GGA+DMFT results exhibits a lattice instability for the transverse (1 1 1) phonon mode. Moreover the amplitude of this lattice instability is consistent with the experimental temperature of stability of this phase. Our calculation thus shows that when the δ phase is thermodynamically unstable (at 0 K), it is also dynamically unstable.

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Section: Introductionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 88%

A unified and efficient theory for the structural properties of actinides and phases of plutonium

Amadon

Dorado

2018

J. Phys.: Condens. Matter

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“…In Ce, for example, the valence fluctuation temperature is reported to reach between 2000 and 5000 K (depending on the applied pressure) within its smallest volume α phase 27,28 . Increased dynamical instability of the δ -phase lattice with increasing x is another possible factor affecting phase stability 59 , although the energies involved appear to be small compared to and .…”

Section: Methodsmentioning

confidence: 99%

Phase stabilization by electronic entropy in plutonium

et al. 2019

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Plutonium metal undergoes an anomalously large 25% collapse in volume from its largest volume δ phase ( δ -Pu) to its low temperature α phase, yet the underlying thermodynamic mechanism has largely remained a mystery. Here we use magnetostriction measurements to isolate a previously hidden yet substantial electronic contribution to the entropy of δ -Pu, which we show to be crucial for the stabilization of this phase. The entropy originates from two competing instabilities of the 5 f -electron shell, which we show to drive the volume of Pu in opposing directions, depending on the temperature and volume. Using calorimetry measurements, we establish a robust thermodynamic connection between the two excitation energies, the atomic volume, and the previously reported excess entropy of δ -Pu at elevated temperatures.

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“…DFPT is not as widely available as the ubiquitous Hellman-Feynman forces, and therefore DFPT may not be available for all codes or basis sets in practice. Furthermore, DFPT often does not support even simple beyond DFT methods such as DFT+U, and at present we are only aware of several examples in the literature 13,14 . Therefore, DFPT is not always an option for second order derivatives.…”

Section: Perturbation Theorymentioning

confidence: 99%

“…However, not all mainstream DFT codes have fully implemented DFPT yet. Moreover, perturbation theory is not ubiquitous for techniques which go beyond DFT, and even simple approaches like DFT+U only have a few demonstrations to date where perturbation theory has been executed at second order 13,14 . Therefore, both perturbation theory and finite displacement approaches will continue to play an important role for the foreseeable future in the context of computing phonons and their interactions.…”

Section: Introduction a General Backgroundmentioning

confidence: 99%

Group theoretical approach to computing phonons and their interactions

Kornbluth

Cheng

et al. 2019

Phys. Rev. B

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Phonons and their interactions are necessary for determining a wide range of materials properties. Here we present four independent advances which facilitate the computation of phonons and their interactions from first-principles. First, we implement a group-theoretical approach to construct the order N Taylor series of a d-dimensional crystal purely in terms of space group irreducible derivatives (ID), which guarantees symmetry by construction and allows for a practical means of communicating and storing phonons and their interactions. Second, we prove that the smallest possible supercell which accommodates N given wavevectors in a d-dimensional crystal is determined using the Smith Normal Form of the matrix formed from the corresponding wavevectors; resulting in negligible computational cost to find said supercell, in addition to providing the maximum required multiplicity for uniform supercells at arbitrary N and d. Third, we develop a series of finite displacement methodologies to compute phonons and their interactions which exploit the first two developments: lone and bundled irreducible derivative (LID and BID) approaches. LID computes a single ID, or as few as possible, at a time in the smallest supercell possible, while BID exploits perturbative derivatives for some order less than N (e.g. Hellman-Feynman forces) in order to extract all ID in the smallest possible supercells using the fewest possible computations. Finally, we derive an equation for the order N volume derivatives of the phonons in terms of the order N = N + 2 ID. Given that the former are easily computed, they can be used as a stringent, infinite ranged test of the ID. Our general framework is illustrated on graphene, yielding irreducible phonon interactions to fifth order. Additionally, we provide a cost analysis for the rock-salt structure at N = 3, demonstrating a massive speedup compared to popular finite displacement methods in the literature.

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Influence of point defects and impurities on the dynamical stability ofδ-plutonium

Cited by 7 publications

References 69 publications

A unified and efficient theory for the structural properties of actinides and phases of plutonium

A unified and efficient theory for the structural properties of actinides and phases of plutonium

Phase stabilization by electronic entropy in plutonium

Group theoretical approach to computing phonons and their interactions

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