References of "Bousquet, Eric"
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See detailGeometric ferroelectricity in fluoroperovskites
Garcia-Castro, A. C.; Spaldin, Nicola A.; Romero, A. H. et al

in Physical Review B (2014), 89

We used first-principles calculations to investigate the existence and origin of the ferroelectric instability in the ABF3 fluoroperovskites. While the ground states of most ABF3 compounds are ... [more ▼]

We used first-principles calculations to investigate the existence and origin of the ferroelectric instability in the ABF3 fluoroperovskites. While the ground states of most ABF3 compounds are paraelectric (Pnma phase), we find that many fluoroperovskites have a ferroelectric instability in their high-symmetry cubic structure that is of similar amplitude to that commonly found in oxide perovskites. In contrast to the oxides, however, the fluorides have nominal Born effective charges, indicating a different mechanism for the instability.We show that the instability originates from ionic size effects, and is therefore in most cases largely insensitive to pressure and strain, again in contrast to the oxide perovskites. An exception is NaMnF3, where coherent epitaxial strain matching to a substrate with equal in-plane lattice constants destabilizes the bulk Pnma structure, leading to a ferroelectric, and indeed multiferroic, ground state with an unusual polarization/strain response. [less ▲]

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See detailNew developments in artificially layered ferroelectric oxide superlattices
Dawber, Matthew; Bousquet, Eric ULg

in MRS Bulletin (2013), 38

Artifi cially layered superlattices of oxide materials have been intensely investigated for some time, but continue to reveal new potential as a route to advanced functional materials. As well as ... [more ▼]

Artifi cially layered superlattices of oxide materials have been intensely investigated for some time, but continue to reveal new potential as a route to advanced functional materials. As well as considering electrostatics and strain, a more complete picture of the interfaces in these systems also needs to incorporate the possibility of additional structural distortions, electronic redistributions, and complex polarization domain structures. Here we focus on superlattices composed of two perovskite oxide materials, where one is a ferroelectric, and discuss the important interactions between the component materials that determine the behavior of the new artifi cial material. We discuss interfaces both with and without electronic screening. The fi rst class of interface contains technologically relevant ultrathin ferroelectric capacitors and the more recently studied ferroelectric-metal superlattices. In these systems, the infl uence of the ferroelectric polarization decreases rapidly with distance from the interface. By contrast, in systems where the materials adjacent to the ferroelectric layers are dielectrics, the polarization of the ferroelectric layer infl uences the properties of the adjacent layers over a much longer distance, setting the stage for fascinating competition between the properties of the combined materials. [less ▲]

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See detailStrong coupling of Jahn-Teller distortion to oxygen-octahedron rotation and functional properties in epitaxially strained orthorhombic LaMnO3
Lee, Jun Hee; Delaney, Kris; Bousquet, Eric ULg et al

in Physical Review. B, Condensed Matter and Materials Physics (2013), 88

First-principles calculations reveal a large cooperative coupling of Jahn-Teller (JT) distortion to oxygenoctahedron rotations in perovskite LaMnO3. The combination of the two distortions is responsible ... [more ▼]

First-principles calculations reveal a large cooperative coupling of Jahn-Teller (JT) distortion to oxygenoctahedron rotations in perovskite LaMnO3. The combination of the two distortions is responsible for stabilizing the strongly orthorhombic A-AFM insulating (I ) eP bnm ground state relative to a metallic ferromagnetic (FM-M) phase. However, epitaxial strain due to coherent matching to a crystalline substrate can change the relative stability of the two states. In particular, coherent matching to a square-lattice substrate favors the less orthorhombic FM-M phase, with the A-AFM phase stabilized at higher values of tensile epitaxial strain due to its larger volume per formula unit, resulting in a coupled magnetic and metal-insulator transition at a critical strain close to 1%. At the phase boundary, a very large magnetoresistance is expected. Tensile epitaxial strain enhances the JT distortion and opens the band gap in the A-AFM-I c-eP bnm phase, offering the opportunity for band-gap engineering. Compressive epitaxial strain induces a transition within the FM-M phase from the c-eP bnm orientation to the ab-eP bnm orientation with a change in the direction of the magnetic easy axis relative to the substrate, yielding strain-controlled magnetization at the phase boundary. Similar behavior is expected in other JT active Pbnm perovskites. [less ▲]

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See detailMonopole-based formalism for the diagonal magnetoelectric response
Spaldin, Nicola A.; Fechner, Michael; Bousquet, Eric ULg et al

in Physical Review. B, Condensed Matter and Materials Physics (2013), 88

We develop the formalism of the macroscopic monopolization—that is, the magnetoelectric monopole moment per unit volume—in periodic solids, and discuss its relationship to the magnetoelectric effect. For ... [more ▼]

We develop the formalism of the macroscopic monopolization—that is, the magnetoelectric monopole moment per unit volume—in periodic solids, and discuss its relationship to the magnetoelectric effect. For the series of lithium transition metal phosphate compounds, we use first-principles density functional theory to calculate the contributions to the macroscopic monopolization from the global distribution of magnetic moments within the unit cell, as well as from the distribution of magnetization around the atomic sites. We find one example within the series (LiMnPO4) that shows a macroscopic monopolization corresponding to a ferromonopolar ordering consistent with its diagonal magnetoelectric response. The other members of the series (LiMPO4, with M=Co, Fe, and Ni) have zero net monopolization but have antiferromonopolar orderings that should lead to q-dependent diagonal magnetoelectric effects. [less ▲]

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See detailFirst-principles study of the ferroelectric Aurivillius phase Bi2WO6
Djani-Ait, Hania ULg; Bousquet, Eric ULg; Kellou, Abdelhafid et al

in Physical Review. B, Condensed Matter and Materials Physics (2012), 86

In order to better understand the reconstructive ferroelectric-paraelectric transition of Bi2WO6, which is unusual within the Aurivillius family of compounds, we performed first-principles calculations of ... [more ▼]

In order to better understand the reconstructive ferroelectric-paraelectric transition of Bi2WO6, which is unusual within the Aurivillius family of compounds, we performed first-principles calculations of the dielectric and dynamical properties of two possible high-temperature paraelectric structures—the monoclinic phase of A2/m symmetry observed experimentally and the tetragonal phase of I4/mmm symmetry—common to most Aurivillius-phase components. Both paraelectric structures exhibit various unstable modes, which, after their condensation, bring the system toward more stable structures of lower symmetry. The calculations confirm that, starting from the paraelectric A2/m phase at high temperatures, the system must undergo a reconstructive transition to reach the P21ab ferroelectric ground state. [less ▲]

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See detailFirst-principles study of structural and vibrational properties of SrZrO3
Amisi, Safari ULg; Bousquet, Eric ULg; Katcho, Karume et al

in Physical Review. B, Condensed Matter and Materials Physics (2012), 85

Using first-principles calculations, we investigate the electronic, structural, and vibrational properties of SrZrO3. We start from the high-symmetry cubic perovskite phase, for which the phonon ... [more ▼]

Using first-principles calculations, we investigate the electronic, structural, and vibrational properties of SrZrO3. We start from the high-symmetry cubic perovskite phase, for which the phonon dispersion curves are reported.We point out the coexistence of structural antiferrodistortive instabilities at the R and M zone-boundary points and a ferroelectric instability at the zone center.We showthat the strong antiferrodistortive motions suppress ferroelectricity and are responsible for the orthorhombic ground state as in CaTiO3. The structural properties <br />of possible intermediate phases and of the orthorhombic Pnma ground state are reported. For the latter, an assignment of IR and Raman zone-center phonon modes is proposed. The main features of the ferroelectric instability are also discussed, and we show that a ferroelectric ground state can even be induced in SrZrO3 by strain engineering. [less ▲]

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See detailPhenomenological thermodynamic potential for CaTiO3 single crystals
Gu, Yijia; Rabe, Karin; Bousquet, Eric ULg et al

in Physical Review B (2012), 85

The antiferrodistortive (AFD) structural transitions of calcium titanate (CaTiO3) at ambient pressure have been extensively studied during the last few years. It has been found that none of the AFD ... [more ▼]

The antiferrodistortive (AFD) structural transitions of calcium titanate (CaTiO3) at ambient pressure have been extensively studied during the last few years. It has been found that none of the AFD polymorphs is polar or ferroelectric. However, it was recently shown theoretically and later experimentally confirmed that a ferroelectric transition in CaTiO3 can be induced by tensile strains. The ferroelectric instability is believed to be strongly coupled to the AFD soft modes. In this paper, we present a complete thermodynamic potential for describing the coupling between the AFD and ferroelectric phase transitions. We analyzed the dependence of transition temperatures on stress and strain condition. Based on this potential, a (001) CaTiO3 thin film diagram was constructed. The results show good agreement with available experimental observations. The strong suppression of ferroelectric transition by the AFD transition is discussed. [less ▲]

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See detailIncipient ferroelectricity in 2.3% tensile-strained CaMnO3 films
Günter, T.; Bousquet, Eric ULg; David, A. et al

in Physical Review. B, Condensed Matter and Materials Physics (2012), 85

Epitaxial CaMnO3 films grown with 2.3% tensile strain on (001)-oriented LaAlO3 substrates are found to be incipiently ferroelectric below 25 K. Optical second harmonic generation (SHG) was used for the ... [more ▼]

Epitaxial CaMnO3 films grown with 2.3% tensile strain on (001)-oriented LaAlO3 substrates are found to be incipiently ferroelectric below 25 K. Optical second harmonic generation (SHG) was used for the detection of the incipient polarization. The SHG analysis reveals that CaMnO3 crystallites with in-plane orientation of the orthorhombic b axis contribute to an electric polarization oriented along the orthorhombic a (respectively c) axis in agreement with the predictions from density functional calculations. [less ▲]

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See detailLinear magnetoelectric effect by orbital magnetism
Scaramucci, A.; Bousquet, Eric ULg; Fechner, M. et al

in Physical Review Letters (2012), 109(19),

We use symmetry analysis and first-principles calculations to show that the linear magnetoelectric effect can originate from the response of orbital magnetic moments to the polar distortions induced by an ... [more ▼]

We use symmetry analysis and first-principles calculations to show that the linear magnetoelectric effect can originate from the response of orbital magnetic moments to the polar distortions induced by an applied electric field. Using LiFePO 4 as a model compound we show that spin-orbit coupling partially lifts the quenching of the 3d orbitals and causes small orbital magnetic moments (μ (L)≈0.3μ B) parallel to the spins of the Fe2 + ions. An applied electric field E modifies the size of these orbital magnetic moments inducing a net magnetization linear in E. © 2012 American Physical Society. [less ▲]

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See detailNoncollinear magnetism and single-ion anisotropy in multiferroic perovskites
Weingart, C.; Spaldin, N.; Bousquet, Eric ULg

in Physical Review. B, Condensed Matter and Materials Physics (2012), 86(9),

The link between the crystal distortions of the perovskite structure and the magnetic exchange interaction, the single-ion anisotropy (SIA), and the Dzyaloshinsky-Moriya (DM) interaction are investigated ... [more ▼]

The link between the crystal distortions of the perovskite structure and the magnetic exchange interaction, the single-ion anisotropy (SIA), and the Dzyaloshinsky-Moriya (DM) interaction are investigated by means of density functional calculations. Using BiFeO 3 and LaFeO 3 as model systems, we quantify the relationship between the oxygen octahedra rotations, the ferroelectricity, and the weak ferromagnetism (wFM). We recover the fact that the wFM is due to the DM interaction induced by the oxygen octahedra rotations. We find a simple relationship between the wFM, the oxygen rotation amplitude, and the ratio between the DM vector and the exchange parameter such that the wFM increases with the oxygen octahedra rotation when the SIA does not compete with the DM forces induced on the spins. Unexpectedly, we also find that in spite of the d5 electronic configuration of Fe3 +, the SIA is very large in some structures and is surprisingly strongly sensitive to the chemistry of the A-site cation of the ABO 3 perovskite. In the ground R3c state phase we show that the SIA shape induced by the ferroelectricity and the oxygen octahedra rotations are in competition such that it is possible to turn the wFM "on" and "off" through the relative size of the two types of distortion. © 2012 American Physical Society. [less ▲]

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See detailUnexpectedly Large Electronic Contribution to Linear Magnetoelectricity
Bousquet, Eric ULg; Spaldin, Nicola A; Delaney, Kris T

in Physical Review Letters (2011), 106(10),

We show that the electronic part of the linear magnetoelectric response, usually omitted in first-principles studies, can be comparable in magnitude to that mediated by polar lattice distortions, even in ... [more ▼]

We show that the electronic part of the linear magnetoelectric response, usually omitted in first-principles studies, can be comparable in magnitude to that mediated by polar lattice distortions, even in strong magnetoelectrics. Using a self-consistent response to a Zeeman field for noncollinear spins, we show how polarization emerges in magnetoelectrics through both electronic and lattice contributions-analogous to the high- and low-frequency responses of dielectrics. The approach we use is computationally simple, and can be used to study linear and nonlinear responses to magnetic fields. [less ▲]

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See detailInduced Magnetoelectric Response in Pnma Perovskites
Bousquet, Eric ULg; Spaldin, Nicola

in Physical Review Letters (2011), 107(19),

We use symmetry analysis to show that the G-, C-, and A-type antiferromagnetic Pnma perovskites can exhibit magnetoelectric (ME) responses when a ferroelectric instability is induced with epitaxial strain ... [more ▼]

We use symmetry analysis to show that the G-, C-, and A-type antiferromagnetic Pnma perovskites can exhibit magnetoelectric (ME) responses when a ferroelectric instability is induced with epitaxial strain. Using first-principles calculations we compute the values of the allowed ME response in strained CaMnO(3) as a model system. Our results show that large linear and non-linear-ME responses are present and can diverge when close to the ferroelectric phase transition. By decomposing the electronic and ionic contributions, we explore the detailed mechanism of the ME response. [less ▲]

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See detailLiMSO(4)F (M = Fe, Co and Ni): promising new positive electrode materials through the DFT microscope
Frayret, Christine; Villesuzanne, Antoine; Spaldin, Nicola et al

in Physical Chemistry Chemical Physics [=PCCP] (2010), 12(47), 15512-15522

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond ... [more ▼]

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond predictions of structural evolution and average voltages versus a lithium electrode, we have applied partial density of states and Bader's topological analysis of the electron density to the study of lithium deintercalation. Upon lithium extraction, charge rearrangement occurs for nickel between different d-orbitals, but with little net positive charge gain, while cobalt and iron atoms end up with a clear oxidized state. The participation of oxygen ions in accepting the electron of the lithium is thus enhanced for LiNiSO(4)F. However, this effect does not affect the long-range electrostatic interactions a lot in the lithiated phase, since the valence of all transition metals is very close due to initial lower oxidized state for the Ni atom in the host. It is found that this is not essentially a long-range electrostatic interaction within the lithiated phase but within the host which explains, at least partly, the increase in voltage by passing from Fe to Ni. Our results also shed light upon the possibility of getting an approximate evaluation of the local strain associated with delithiation from the atomic volume evolutions, which are also likely to affect the electrochemical potential. [less ▲]

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See detailStrain-induced ferroelectricity in simple rocksalt binary oxides
Bousquet, Eric ULg; Spaldin, N.; Ghosez, Philippe ULg

in Physical Review Letters (2010), 104

Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial ... [more ▼]

Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial strains. Going beyond the fundamental discovery, we highlight that the functional properties (polarization, dielectric constant, and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, making them of direct interest for applications. Finally, we show that magnetic binary oxides such as EuO, with the same rocksalt structure, behave similarly to the alkaline-earth-metal oxides, suggesting a route to new multiferroics combining ferroelectric and magnetic properties. [less ▲]

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See detailFirst-principles study of competing ferroelectric and antiferroelectric instabilities in BaTiO3/BaO superlattices
Bousquet, Eric ULg; Junquera, Javier; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2010), 82

We report a first-principles study of (BaTiO3) m/ (BaO) n superlattices for a wide range of periodicities m/n. We show that such a system develops a polar zone-center instability for sufficiently large m ... [more ▼]

We report a first-principles study of (BaTiO3) m/ (BaO) n superlattices for a wide range of periodicities m/n. We show that such a system develops a polar zone-center instability for sufficiently large m/n ratio, which can be understood, at least qualitatively, from a simple electrostatic model and should lead to a ferroelectric ground state. However, the analysis of the phonon-dispersion curves also points out the appearance of stronger antiferroelectric instabilities at the zone boundaries around m=4, before the critical ratio for ferroelectricity is reached and which still dominate beyond it. The dominant character of the antiferroelectric instability is explained from the depolarizing field which hardens the ferroelectric mode. This analysis allows us to predict that, (BaTiO3) m/ (BaO) n superlattices should present an antiferroelectric ground state for m larger than 4, which should smoothly evolve to a multidomain structure for increasing m values and only become ferroelectric for large m. [less ▲]

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See detailJ dependence in the LSDA plus U treatment of noncollinear magnets
Bousquet, Eric ULg; Spaldin, Nicola

in Physical Review. B, Condensed Matter and Materials Physics (2010), 82(22),

We re-examine the commonly used density-functional theory plus Hubbard U (DFT+U) method for the case of noncollinear magnets. While many studies neglect to explicitly include the exchange-correction ... [more ▼]

We re-examine the commonly used density-functional theory plus Hubbard U (DFT+U) method for the case of noncollinear magnets. While many studies neglect to explicitly include the exchange-correction parameter J, or consider its exact value to be unimportant, here we show that in the case of noncollinear magnetism calculations the J parameter can strongly affect the magnetic ground state. We illustrate the strong J dependence of magnetic canting and magnetocrystalline anisotropy by calculating trends in the magnetic lithium orthophosphate family LiMPO(4) (M=Fe and Ni) and difluorite family MF(2) (M=Mn, Fe, Co, and Ni). Our results can be readily understood by expanding the usual DFT+U equations within the spinor scheme, in which the J parameter acts directly on the off-diagonal components which determine the spin canting. [less ▲]

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See detailEngineering Multiferroism in CaMnO3
Bhattacharjee, Satadeep; Bousquet, Eric ULg; Ghosez, Philippe ULg

in Physical Review Letters (2009), 102

Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic ... [more ▼]

Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic perovskite structure of CaMnO3 also exhibits a weak ferroelectric instability. Although ferroelectricity is suppressed by antiferrodistortive motions, we show that it can be favored using strain or chemical engineering in order to make CaMnO3 multiferroic. We finally highlight that the ferroelectric instability of CaMnO3 is Mn-dominated. This illustrates that, contrary to common belief, ferroelectricity and magnetism are not necessarily exclusive but can be driven by the same cation. [less ▲]

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See detailCorrelation between optical constants and crystal chemical parameters of ZrW2O8
Shannon, Robert D; Fischer, Reinhard X; Medenbach, Olaf et al

in Journal of Solid State Chemistry (2009), 182(10), 2762-2768

The refractive indices of ZrW2O8, measured at wavelengths of 435.8-643.8 nm, were used to calculate n(D) at lambda = 589.3 nm and n(infinity) at lambda = infinity from a one-term Sellmeier equation ... [more ▼]

The refractive indices of ZrW2O8, measured at wavelengths of 435.8-643.8 nm, were used to calculate n(D) at lambda = 589.3 nm and n(infinity) at lambda = infinity from a one-term Sellmeier equation. Refractive indices, n(D) and dispersion values, A, are, respectively, 1.8794 and 114 x 10(-16) m(2). The high dispersion, relative to other molybdates, tungstates and Zr-containing compounds, is attributed to the low value of E-o = 7.7 eV and mean cation coordination number. Total electronic polarizabilities, alpha(total), were calculated from n(infinity) and the Lorenz-Lorentz equation. The unusually large difference between the observed polarizability of 20.087 angstrom(3) and the calculated total polarizability alpha(T) of 17.59 angstrom(3) (Delta = +12.4%) is attributed to (1) a large M-O-W angle, (2) a high degree of W 5d-O(terminal) 2p and Zr nd-O 2p hybridization, and (3) unusually high oxygen displacement factors, B(O), normalized to B(W). (C) 2009 Elsevier Inc. All rights reserved. [less ▲]

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See detailFirst-principles study of the dielectric and dynamical properties of orthorhombic CaMnO3
Bhattacharjee, Satadeep; Bousquet, Eric ULg; Ghosez, Philippe ULg

in Journal of Physics : Condensed Matter (2008), 20

The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory ... [more ▼]

The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory approach within the local spin density approximation. The theoretical structural parameters are in good agreement with experiment. The full set of zone-center phonons is reported, allowing new assignment of experimental Raman data and providing reference values for the interpretation of future infrared phonon measurements. It is shown that the static dielectric constant is very large and comparable in amplitude to that of isostructural CaTiO3. In contrast to the pseudocubic structure, it is also highly anisotropic. These features are discussed in relationship to the anomalous Born effective charges and the presence of low frequency polar modes. [less ▲]

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See detailNew insight into the concept of ferroelectric correlation volume
Geneste, Gregory; Bousquet, Eric ULg; Ghosez, Philippe ULg

in Journal Of Computational And Theoretical Nanoscience (2008), 5(4), 517-520

Using an effective Hamiltonian derived from first-principles calculations, we discuss the concept of "ferroelectric correlation volume" and show that it cannot be uniquely defined: it is not the size but ... [more ▼]

Using an effective Hamiltonian derived from first-principles calculations, we discuss the concept of "ferroelectric correlation volume" and show that it cannot be uniquely defined: it is not the size but the anisotropic shape of the polar region that is crucial for stabilizing a ferroelectric distortion into a ferroelectric materials. To provide basic understanding of this result, the stability of a polar region is analyzed in term of intra-chain and inter-chain interactions. [less ▲]

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