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International audience; The use of broken-symmetry calculations in Kohn–Sham density functional theory has offered an affordable route to study magnetic exchange couplings in transition-metal-based compounds. However, computing this property in compounds exhibiting several couplings is still challenging and especially due to the difficulties to overcome the well-known problem of spin contamination. Here, we present a new and general method to compute magnetic exchange couplings in systems featuring several spin sites. To provide a consistent spin decontamination of J values, our strategy exploits the decomposition method of the magnetic exchange coupling proposed by Coulaud et al. and generalizes our previous work on diradical compounds where the overall magnetic exchange coupling is defined as the sum of its three main and properly extracted physical contributions (direct exchange, kinetic exchange, and spin polarization). In this aim, the generalized extraction of all contributions is presented to systems with multiple spin sites bearing one unpaired electron. This is done by proposing a new paradigm to treat the kinetic exchange contribution, which proceeds through monorelaxations of the magnetic orbitals. This method, so-called the recomposition method, is applied to a compound featuring three Cu(II) ions with a linear arrangement and to a recently synthesized complex containing a Cu4O4 cubane unit presenting an unusual magnetic behavior.

International audience; Providing tools to understand the physical mechanisms governing magnetic properties in transition metal-based compounds is still of great interest. Here, the magnetic exchange coupling in a series of heterodinuclear complexes is investigated by means of the decomposition method. This work presents the first application of the decomposition method to systems where magnetic centres may bear more than one unpaired electron. By decomposing the coupling into three physical contributions (direct exchange, kinetic exchange, and spin polarisation), we provide numerical arguments to confirm or infirm the rationalisation allowed by the conceptual analysis of the magnetic d orbitals. We also take advantage of the recently proposed generalisation of the method [David et al., J. Chem. Theory Comput., 2023, 19, 157] to get more insights into the underlying mechanisms by disentangling the coupling between centres into its electron-electron interactions.

International audience; There is a considerable knowledge gap regarding the long-term fate of plastics in the environment. Acknowledging this gap, in the context of life cycle assessment methods, is critical to account for the long-term fate of plastics in the decision-making process. Ignoring the long-term potential for environmental and health damage from plastic particles makes it difficult to defend a quantitative environmental assessment comparing fossil-based conventional plastics with other alternative materials. This Review highlights that the addition of a plastic particulate footprint as a midpoint impact indicator in life cycle assessments should be considered to quantify these overlooked long-term impacts

Two winery residues, namely vine shoots (ViSh) and wine pomace (WiPo), were up-cycled as fillers in PHBV-based biocomposites. Answering a biorefinery approach, the impact of a preliminary polyphenols extraction step using an acetone/water mixture on the reinforcing effect of fillers was assessed. Biocomposites (filler content up to 20 wt%) were prepared by melt-mixing and compared in terms of final performance (thermal, mechanical and barrier). It was shown that the reinforcing effect was slightly better in the case of vine shoots, while it was not significantly affected by the pre-treatment, demonstrating that these two winery residues could be perfectly used as fillers in composite materials even after an extraction process to maximize their potential of valorization.

An efficient implementation of geometrical derivatives at the Hartree-Fock (HF) and current-density functional theory (CDFT) levels is presented for the study of molecular structure in strong magnetic fields. The required integral derivatives are constructed using a hybrid McMurchie-Davidson and Rys quadrature approach, which combines the amenability of the former to the evaluation of derivative integrals with the efficiency of the latter for basis sets with high angular momentum. In addition to its application to evaluating derivatives of four-center integrals, this approach is also applied to gradients using the resolution-of-the-identity approximation, enabling efficient optimization of molecular structure for many-electron systems under a strong magnetic field. The CDFT contributions have been implemented for a wide range of density functionals up to and including the meta-GGA level with current-density dependent contributions and (range-separated) hybrids for the first time. Illustrative applications are presented to the OH and benzene molecules, revealing the rich and complex chemistry induced by the presence of an external magnetic field. Challenges for geometry optimization in strong fields are highlighted, along with the requirement for careful analysis of the resulting electronic structure at each stationary point. The importance of correlation effects is examined by comparison of results at the HF and CDFT levels. The present implementation of molecular gradients at the CDFT level provides a cost-effective approach to the study of molecular structure under strong magnetic fields, opening up many new possibilities for the study of chemistry in this regime.

International audience; Background: Graft-versus-host disease (GVHD), particularly acute digestive GVHD (aDGVHD), is a severe complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). It is necessary to identify predictive factors of GVHD to adapt prophylactic treatment.Objective: In this context, our pilot study aimed (i) to determine whether an early remodeling of the colonic mucosa occurred after allo-HSCT and (ii) to identify potential predictive mucosal markers of aDGVHD after allo-HSCT.Methods: Between day 21 and day 28 after the allo-HSCT, 19 allo-HSCT patients were included and had a rectosigmoidoscopy with probe-based confocal laser endomicroscopy (pCLE) recording and biopsies. Sixteen patients were included in the control group. Morphological (pCLE), functional (intestinal permeability), and inflammatory parameters (cytokine multiplex immunoassay) were assessed.Results: Among allo-HSCT patients, 11 patients developed GVHD, and 6 of them developed aDGVHD. Morphological and functional changes of the colonic mucosa occurred after allo-HSCT. Indeed, the perimeter of colonic crypts was significantly increased in allo-HSCT patients compared to controls as well as crypt lumen fluorescein leakage (53% vs. 9%), whereas crypts sphericity, roundness, Feret diameter, and mean vessel area were significantly decreased in allo-HSCT patients compared to the control group. In addition, interleukin-6 (IL-6), IL-33, and IL-15 levels in the supernatants of 24 h explant cultures of colonic biopsies were significantly increased in allo-HSCT patients compared to controls. Finally, there was no difference in pCLE parameters, intestinal permeability, and inflammatory cytokines between patients who developed aDGVHD and those who did not.Conclusion: This pilot study identified early colonic mucosa remodeling after allo-HSCT conditioning therapy, that is morphological and functional mucosal alterations as well as mucosal inflammation. As to whether these changes are first steps in GVHD initiation and could be considered as predictive biomarkers of aDGVHD need to be determined in a larger cohort of patients.

International audience; Spin-polarization effects may play an important role in free radicals and in the magnetic coupling between radical centers. Starting from restricted open-shell calculations, i.e. a closed-shell description of the non-magnetic core electrons, a low-order perturbation expansion identifies the spin polarization contribution to the energy of mono-radicals and to singlet-triplet energy differences in diradicals. Broken-symmetry (BS) single-determinant calculations introduce only a fraction of spin polarization effects, and in a biased manner, since BS determinants are not spin eigenfunctions. We propose a simple technique to correctly evaluate spin-polarization energies by taking into account the effect of spin-flip components of one-hole one-particle excited configurations. Spin-decontamination corrections is shown to play a non-negligible role in BS evaluation of bond energies. The importance of spin-decontamination is illustrated on cases for which spin polarization is the leading contribution to the singlet-triplet gap, what characterizes twisted conjugated double-bonds and disjoint diradicals.

Vine shoots are lignocellulosic agricultural residues. In addition to being an interesting source of polyphenols, they can be used as fillers in a poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV) matrix to decrease the overall cost and to propose an alternative to non-biodegradable fossil-based materials. The objective of the present work was to investigate how the incorporation of vine shoots fillers and a preliminary polyphenol extraction step could impact the biodegradability of biocomposites. Biocomposites (20 wt %) were produced by microcompounding. The biodegradation of materials was assessed by respirometric tests in soil. The negative impact of polyphenols on the biodegradability of vine shoots was confirmed. This was supported by crystallinity measurements and scanning electron microscopy (SEM) observations, which showed no difference in structure nor morphology between virgin and exhausted vine shoots particles. The incorporation of vine shoots fillers in PHBV slightly accelerated the overall biodegradation kinetics. All the biocomposites produced were considered fully biodegradable according to the French and European standard NF EN 17033, allowing the conclusion that up-cycling vine shoots for the production of lignocellulosic fillers is a promising strategy to provide biodegradable materials in natural conditions. Moreover, in a biorefinery context, polyphenol extraction from vine shoots has the advantage of improving their biodegradability.

International audience

International audience

International audience

International audience; In order to lift the barrier of a poor interfacial interaction between cellulosic plant fibers and polymeric matrices in biocomposites, an eco-friendly surface modification of fibers was explored. A solvent-free gas-phase ester-ification applied to cellulose particles allowed to graft palmitoyl moieties on their surface in order to make them more compatible with non-polar polymers for composite applications. The efficiency of the treatment was evidenced from FT-IR analysis, and the degree of substitution (DS) was quantified by solid-state 13 C NMR spectroscopy. The effect of surface grafting on resulting intrinsic characteristics of cellulose particles, i.e. crys-tallinity, thermal stability, morphology, surface free energy and water vapor sorption were investigated respectively by X-ray diffraction, thermogravimetric analysis, SEM observations coupled with image analysis, contact angle measurements and dynamic vapor sorption system (DVS). It was shown that a DS as low as 0.01 was enough to drastically increase the hydrophobicity of cellulose particles without affecting the inner properties of cellulose.

International audience; Many nanoporous solids (e.g. activated carbons, zeolites, MOFs) can exhibit non- monotonic deformation upon adsorption, alternating between contraction and expansion stages according to the thermodynamic conditions and pore sizes. The case of water is particularly interesting, not only for its importance in many industrial applications and natural processes, but also because the adsorptive behaviour of this latter is complex and presents varied mechanisms. This study aims at characterising the adsorption-induced pore pressure of water in nanoscopic slit pores by molecular non-local density functional theory (DFT). The DFT is coupled with the statistical associative fluid theory for potential of variable range (SAFT-VR) which is highly accurate for the modelling of the bulk phase and equilibrium thermodynamic properties of water. This SAFT-DFT coupling has already been applied to methane confined in graphitic slit- like nanopores. While retaining the accuracy of molecular simulations at pore scale, the model has a very low computational cost that allowed obtaining highly resolved pore pressure maps as a function of both pore width and thermodynamic conditions.In this work, several configurations are explored for confined water by changing both the thermodynamic conditions and the pore sizes. For instance, the capillary condensation and evaporation are investigated with the theoretical model in micro- and mesopores. The adsorption hysteresis gives rise to a pressure hysteresis for which consequences on the mechanical behaviour are investigated. The influence of the surface activation on water adsorption and pore pressure is also explored.

International audience

International audience; Using broken-symmetry Kohn-Sham Density-Functional Theory calculations, it is demonstrated that the ferromagnetic or anti-ferromagnetic character of two prototyp-ical binuclear copper complexes can be modified, both in the sign and in magnitude, by means of chemical substitutions operated on the bridges connecting the two magnetic centers. The level of detail provided by the magnetic exchange decomposition in terms of direct exchange, kinetic exchange and core polarization puts forward the relative importance of the different bridges. At variance with the principal bridge for which chemical substitutions modify both the direct and the kinetic exchange contributions , modifications of the secondary bridge only affect the magnitude of the anti-ferromagnetic kinetic exchange mechanism, ultimately allowing for a direct control of the magnetic character of the modified compound.

COM; International audience; Raman (micro)-spectroscopy and X-ray fluorescence spectrometry are powerful analytical techniques that allow for molecular and elemental analysis, respectively. These types of characterizations are essential to identify the salt or mix of salts responsible for the weathering of stones, bricks and mortars. Due to the evolving nature of salts, the process of sample extraction and storage in laboratory might alter the state of the degradation and lead to erroneous assumptions. Recent advances allowed for the development of portable devices for both x-ray fluorescence and Raman spectroscopy, which avoids these problems because they allow to perform measurements in-situ. Still, the use of miniaturized equipment involves sacrifices concerning the spectral resolution and geometrical precision. Here, a comparison is presented between in-situ and laboratory analysis to ascertain the amount and importance of loss of information caused by the change of method. The object of study was a 130 year old structure, the Villa Belza, located at the coast of Biarritz, France. The analysed façade suffered from severe weathering of different building materials, in-situ analysis were performed in nine different points, including natural stone, building stone and mortar. Subsequently, cores were drilled in each of these locations and transported to the laboratory for further study. The identification of elements and molecules by the proposed techniques is weighted against their importance as forensic tools and conclusions are drawn regarding the necessary accuracy for the case of the Villa Belza. The authors concluded that the difference in information quality could be diminished by altering acquisition parameters, and in-situ techniques were sufficient for the porposition of damage mechanisms.

AFF; International audience; Size effect is a known problem of mechanics affecting the extrapolation of laboratory results into conclusions regarding full structures. In the context of salt weathering, a gap exists between the understanding of the crystallization of a single crystal in a controlled environment and the damage of porous material due to a zone of coalescence of such process. The recent advances in quantitative x-ray micro-tomography analysis has been a step forward in the comprehension of precipitation damage in porous media. However, given the scale of the process, a search for ever higher resolution motivates the use of smaller samples. While the use of samples measuring few milimetres or even micrometers is useful for the visualization of different phases of the damage cycle, it might not be representative of the process taking place in full size pieces. We present data on the influence of sample dimension on the process of salt damage. Cylindrical samples of Lavoux limestone were prepared in four sizes (4x8 mm, 8x16 mm, 25x50 mm, 50x50 mm) and subjected to wet-and-dry cycles until the onset of damage. All samples were sealed in all faces except the upper side. During each cycle, a 3,4 weight % sodium chloride solution was dispensed on the free face in an amount equivalent to 60% of the volume of the respective porous space. The samples were kept for one hour at laboratory conditions (T=22ºC; RH=60%) allowing for the solution to penetrate the sample. Subsequently, a 23 hours drying step was carried out at 40 ºC and 40% relative humidity. At the end of the weathering, quantitative x-ray micro-tomographies were compared with prior scans of the samples in their unweathered state to assess the deterioration in all sizes of samples. The assessment of the relation between sample size and sample damage should highlight the limitations of the use of very small samples.

AFF; International audience; One century ago, Stephen Taber mentioned that the crystallisation pressure could play a role in geological settings, but to now no experimental data could really prove it in a clear way [1]. Our goal is to come up with an experiment that clearly demonstrate the potential of crystallisation pressure as a fracture inducer in geological settings. Data on the salt precipitation and distribution in the pore space of a confined and saturated limestone sample are presented, as well as the damaging character of this precipitation. For this purpose, two different experiments were designed and set up. The first one focuses on the precipitation of barite studied in a system involving the contra diffusion of Ba2+ and SO42- rich solutions in a cylindrical sample of Lavoux limestone. The second one aims at creating a localised mirabilite precipitation front in the same type of cylindrical Lavoux specimen. To that extent, cooling cycles are imposed on the sample saturated with an aqueous Na2SO4 solution. The experiments are monitored with video acquisition and temperature sensors to measure sample swelling or temperature change due to crystallisation. The post treatment consists in 3D X-ray micro-tomographic scans of the damaged sample conducted at the UPPA Centre for X-ray Imaging DMEX together with thin sections of relevant features. Depending on the first results, we may show additional data of experiments monitored with an acoustic set up in order to listen to the acoustic emission created by crystallisation and fracturing events. This allows localizing the cracks epicenter and the damage zone.

International audience; Spin-symmetry breaking appears in the DFT treatment of polyacenes, beyond a certain length, the critical length depending on the exchange-correlation potential. This phenomenon may be attributed to an instability with respect to HOMO–LUMO mixing, which suggests a diradical character of long acenes. However, the increase of the S2 operator with acene length questions this simple view. It is shown that this increase cannot be attributed to spin polarization of the inner MOs, and that a second symmetry breaking takes place for the pentadecacene, with four unpaired electrons centered at the first and third quarters of the chain. The spin density distributions of broken-symmetry solutions support a qualitative picture in terms of tetra-methylene hexacenes separated by Clar sextets. A strategy is proposed to identify local symmetry breaking in polyradical systems.

International audience

International audience; Analytical expressions of the interactions present in the Heisenberg–Dirac van Vleck and Hubbard Hamiltonians have been derived as functions of both the energy of several broken symmetry DFT solutions and their expectation value of the S2 spin operator. Then, following a strategy of decomposition of the magnetic exchange coupling into its main contributions (direct exchange, kinetic exchange, and spin polarization) and using a recently proposed method of spin decontamination, values of these interactions have been extracted. As already observed, they weakly depend on the correlation functional but strongly depend on the exchange one. In order to distinguish between the effect of the delocalization of the magnetic orbitals and that of the amount of Hartree–Fock exchange (HFX) when hybrid exchange-correlation functionals are used, we have disentangled these two contributions by either freezing the magnetic orbitals and varying the amount of HFX or varying the magnetic orbitals while keeping the same amount of HFX. As expected, increasing the amount of HFX induces a slight relocalization of the magnetic orbitals on the magnetic center which results in a weak increase of the repulsion energy U parameter and a weak decrease of both the direct exchange Kab and hopping |t| parameters. Conversely, the amount of HFX has a huge effect on all the parameters, even when some of the parameters should be exchange-independent, like U. Indeed, it is analytically demonstrated that the physical content of the U parameter extracted from several broken-symmetry solutions depends on the amount of HFX and that this pathological behavior has the same origin as the self-interaction error. This result is interesting not only to theoretical chemists working in the field of magnetic systems but also to DFT methodologists interested in using this theory for studying either excited states or strongly correlated systems. Finally, the performance of the range-separated ωB97XD functional for both ferromagnetic and antiferromagnetic transition-metal compounds and organic systems must be noted.

International audience

International audience; Characterizing the path of a hydraulic fracture in a heterogeneous/jointed medium is one of the challenges of current research on hydraulic fracturing. We present here a 2D lattice hydro-mechanical model for this purpose. Natural joints are represented by introducing elements with a new plastic-damage behaviour. The action of the fluid pressure on the skeleton is represented by using Biot’s theory. The interactions of cracks on the fluid flow are represented by considering a Poisueille’s flow between two parallel plates. Numerical coupling is achieved with a staggered coupling scheme.

International audience

International audience

International audience

International audience