Ali ZAOUI

Short bio

Position

Scientific activites

- Over 200 publications in international journals (rank A).

- Invited/keynote speaker in more than 70 international conferences.

- Around 30 PhD students already supervised. More than 30 Master students.

- Organizer and/or member of scientific committee for 40 national or international conferences.

- Member of 70 committees of PhD and habilitation mainly in France, Sweden, China, Algeria and Lebanon.

- Editor of :

- Journal of Rock Mechanics and Geotechnical Engineering
- Materials Genome Engineering
- Experimental and Theoretical NANOTECHNOLOGY
- Magnetochemistry

- Current projects :

- Multiscale modeling of advanced nano-reinforced geopolymer/CNTs materials (ANR NanoGP)
- Advanced Nuclear Materials and Radiation Physics. Chinese 111 Project, Beijing (China)
- Creation and development of an innovative industrial ecology and training center for the application of circular economy principles for the building and rail sector. ‘Lille la Délivrance’ (PSPC- Regions project)

Additional information

- Since October 2006-Now: Premium doctoral supervision (PEDR) or Scientific excellence award (PES),always with the highest level (type A).

- Member and Task leader for the action ‘Self-healing As preventive Repair of COncrete Structures’ of ECOST.

- Former Regular associate member of the international center for theoretical physics, Trieste (Italy)

guest professor in foreign universites

Zhenjiang University (Hangzhou, China). Beihang University (Beijing, China). Hohai University, (Nanjing, China). Hunan University (China). SUN Yat-Sen University (China). Uppsala University (Sweden). USTO (Oran, Algeria). Central University of Caracas (Venezuela). ICTP (Trieste, Italy). Max Planck Institute of Halle, Germany. Michigan Technology, (USA).

research responsabilities

-Director of the Laboratory of Civil Engineering and Geo-Environment Laboratory (LGCgE).

-Group leader of Multi-scale modeling and characterization of coupled problems team.

-Since 2015 –until now: Elected member (twice) of the National Council of Universities (Conseil National des Universités, CNU60).

-Since 2015- until now: Elected member of the council of Polytech’Lille.

Teaching administration

-From September 2015 -until now: Director of the international master of nanoscience and nanotechnology for civil engineering (http://master-nngc.univ-lille1.fr).

-Former Director of bachelor and Master department in Polytech'Lille including Civil Engineering, Mechanics and Mechanical engineering.

-Former Responsible of the mechanics field at the university of Lille 1.

-Former Academic director and jury president of Bachelor 2nd et 3rd year for the field of Civil Engineering, mechanics, and mechanical engineering.

-Former Commissioner responsible for recruiting and validation for the bachelor students (2nd et 3rd year), option civil engineering.

-Former Commissioner responsible for recruiting and validation for Master 1students (1st year), option mechanics, civil and mechanics engineering.

-Former Elected member of the 60th section Committee of specialists from the University of Science and Technology of Lille (USTL).

-Former Member of recruitment committee in USTL for the 60th section.

-Former Member of the research committee in Polytech’Lille.

- Reviewing: Proceedings of the National Academy of Sciences of the United States of America (PNAS), Nature-Scientific Reports, Nanoscale, Applied Physics Letters, Journal of Applied Physics, Solid State Communications, Applied Surface Science, Acta Materiala, High pressure research, Semicond. Sci. Technol., Chemistry of Materials, International Journal of Hydrogen Energy, Journal of Alloys and Compounds, The European Physical Journal B, Computational Materials Sciences. Physics Letters A, Infrared Physics and Technology, Materials Letters, Journal of Materials Research, PhysicaB: condensed Matter, Physica Status Solidi (b), Journal of Crystal Growth, Journal of Physics: Condensed Matter, RSC Advances, Journal of Coating technology and research, Current Applied Physics, Computational Condensed Matter European Physical Journal of Applied Physics, European Physical Society, Dalton Transactions, ChemPhysChem, Journal of Materials Sciences, Inorganic Chemistry, Géotechnique, The journal of Physic al Chemistry, Applied Clay Sciences, Cement and Concrete Research, Nanotechnology, ...

Research summary

Professor Ali Zaoui’s multidisciplinary research has been mainly dedicated to the modeling and simulation methods based on first-principles, molecular dynamics and Monte Carlo. They cover a wide range of materials including geo-materials, minerals, clays, cement, asphalt, nano-composites, nanomaterials, polymers, semiconductors and metals. He has published over 200 papers in international journals with high impact factor.

Selected publications

1. W. Sekkal and A. Zaoui, High strength metakaolin-based geopolymer reinforced by pristine and covalent functionalized carbon nanotubes, Construction and Building Materials 327, 11, 126910 (2022).

2. M. Laanaiya, A. Zaoui, Piezoelectric response and failure behavior of cement paste under external loading, Cement and Concrete Research 139, 106257 (2021).

3. W. Sekkal and A. Zaoui, Novel properties of nano-engineered cementitious materials with fullerene buckyballs, Cement and Concrete Composites 118, 103960 (2021).

4. D. Tunega and A. Zaoui, Mechanical and Bonding Behaviors Behind the Bending Mechanism of Kaolinite Clay Layers, J. Phys. Chem. C 124, 13, 7432-7440 (2020).

5. M. Laanaiya, A. Zaoui, Preventing cement-based materials failure by embedding Fe2O3 nanoparticles, Construction and Building Materials 260, 10, 120466 (2020).

6. A.Lushnikova, A. Zaoui, Influence of single-walled carbon nanotubes structure and density on the ductility of cement paste. Construction and Building Materials 172, 86-97 (2018).

7. Y. Zheng and A. Zaoui, Mechanical behavior in hydrated Na-montmorillonite clay. Physica A-Statistical Mechanics and its Applications 505, p. 582–5901 (2018).

8. T. Jefferson, E. Javierre, B. Freeman, A. Zaoui, E. Koenders, L. Ferrara. Research progress on numerical models for self-healing cementitious materials. Advanced Materials Interfaces 5, 1701378 (2018)

9. W. Sekkal and A. Zaoui Enhancing the interfacial bond strength of cement nanocomposite with carbonate nanostructure. Composites Part B 124, 111-119 (2017).

10.Y. Zheng and A. Zaoui, Wetting and nanodroplet contact angle of the clay 2:1 surface: The case of Na-montmorillonite (001). Applied Surface Science 396, 717–722 (2017).

11. W. Sekkal, A. Zaoui, M. Benzerzour, N.E. Abriak, Role of porosity on the stiffness and stability of (001) surface of the nanogranular C-S-H gel. Cement and Concrete Research 87, 45-52 (2016).

12. A. Bouibes and A. Zaoui A route to possible civil engineering materials: the case of high-pressure phases of lime. Nature- Scientific Reports 5, 12330 (2015).

13. W. Yang, Y. Zheng and A. Zaoui, Swelling and diffusion behavior of Na-vermiculite at different hydrated states, Solid State Ionics 282, 13–17 (2015).

14. A. Zaoui and W. Sekkal, Can clays ensure nuclear waste repositories? Nature- Scientific Reports 5, 8815 (2015).

15. A. Zaoui and W. Sekkal, (2014). Mechanisms behind the Ikaite-to-Calcite phase transformation from molecular dynamics calculations. GEODERMA, 235-236, 329-333 (2014).

16. W. Yang and A. Zaoui, Behind adhesion of Uranyl onto Montmorillonite surface: A molecular dynamics study. Journal of Hazardous Materials 261, 224- 234 (2013).

17. B. K. Benazzouz, A. Zaoui and A. B. Belonoshko, Melting temperature of Kaolinite from Z-method. American Mineralogist 98, 1881-1885 (2013).

18. W. Yang and A. Zaoui, Uranyl Adsorption on (001) surfaces of Kaolinite: A Molecular Dynamics Study. Applied Clay Science 80. 98-106 (2013).

19. D. Tunega, T. Bucko, and A. Zaoui, Assessment of ten DFT methods in predicting structures of sheet silicates: importance of dispersion corrections. The Journal of Chemical Physics 137, 114105-114114 (2012).

20. A. Zaoui, Insight into elastic behavior of calcium silicate hydrated oxide (C–S–H) under pressure and composition effect. Cement and concrete research, 42, 306-312 (2012).

Research interests and topics

1. Geopolymer reinforced by pristine and covalent functionalized carbon nanotubes

2. ‘Playing selfy’ in cementitious materials

The stiffness, the durability and high performance properties of concrete are controlled by the principal product of cement hydration and primary binding phase, the calcium silicate hydrate (C–S–H). The way to enhance the macroscopic mechanical properties of hydrated cement is by understanding and modifying the structure of the C–S–H gel at atomic level. Thanks to nanotechnology and nanoscience developments, research may have the potential to engineer concrete with superior mechanical, sensing and durable properties through the use of nanomaterials. These nanomaterials may be classified according to their shape or morphology: zero-dimensional (0D) particles, one-dimensional (1D) fibers and two-dimensional (2D) sheets. Nano-engineering, or nanomodification, of C–S–H at the nanoscale has received attention due to the interest of the layered structure of C-S-H, which offers the potential for creative manipulation by the insertion of a variety of foreign molecules into the basic C–S–H structure. The extraordinary chemical and physical properties of nanomaterials enable novel applications ranging from structural strength enhancement to self-cleaning, self-sensing and self-healing properties.

Self-sensing of concrete

Self-cleaning in concrete

We have studied the durability of concrete, which can be improved with the addition of nano-particles by increasing resistance to water penetration. We have proposed a simulation of a nanodroplet of water on the surface of concrete in order to evaluate the contact angle and measure the degree of hydrophobicity of concrete. We aim also to see the effect of temperature, porosity and water-to-cement ratio on the hydrophobicity and then the durability of concrete. Besides, the variation of the contact angle within the variation of the density and the dispersion of nano fillers in concrete.

Hydrophilic, hydrophobic, overdrophobic, superdrophobic surfaces (De Gennes et al., 2004)

3. Nanomaterials in concrete

Concrete with inserted carbon nanotubes

We have are studying the incorporation of carbon nanotubes in a grain of C-S-H Our results show that the modification of the 11 Å tobermorite by the CNT (3,0) with the diameter 2.35 Å increase all the mechanical parameters such bulk modulus, shear modulus and Young’s modulus at the same time and also give the best adhesion between the structure of C-S-H and CNT’s structure. The effects of diameter dimension and density of nanotubes are taken into account.

Schematic view of contact area between CNT and C-S-H

Structure of the Single Wall Nanotube (a), and Multi Wall Nanotube (b)

a) Zigzag, Armchair formed from graphene sheet, b) Zigzag carbon nanotube, c) Armchair carbon nanotube

Schematic view of the CNT’s insertion into the hole of C-S-H

Nano-engineered concrete with fullerene buckyballs

We evoke the important subject of the improvement of the strength and the durability of the future generation of smart nano-engineered cementitious composites through the incorporation of another kind of nanomaterial like fullerene buckyballs (C60). This research is dedicated to the analysis - at nanoscale - of the processus of embedding C60 nanomaterials in calcium silicate hydrates (C-S-H). Using molecular dynamics simulations, we evaluate the mechanical response with the density and dispersion of fullerene molecules as well as porosity of C-S-H. Under shear stress, the nanostructure shows an increase of the shear strength along x and y directions due to the long silicate chains and Ca-O bond.

CSH enhanced with C60.

Energy versus fullerene concentration

Enhancing durability and stiffness of Cement

We have studied the relationship between bonding and mechanical properties of cementitious mineral tobermorite using ab initio calculations. Calculated bulk modulus and elastic constants reflect a relatively high resistance of hydrated C-S-H with respect to external isostatic compression. We have found, in particular, that the directions parallel to the axb plane are more resistant to the compression than the perpendicular direction. We have also been able to highlight, for the first time, the effect of pressure and composition on C-S-H using lattice dynamics method. Our results show that around 20 GPa an important change appears in the elastic behavior of hydrated C-S-H. As pressure increases the calculated elastic quantities for Ca/Si= 1 became closer to those evaluated for Ca/Si = 0.83.

SEM Image (ref. Galmarini)

Grain of C-S-H (from our studies) Morphology of C-S-H grain

C-S-H/Calcite interface

In a more recent work funded by IMT-Lille-Douai we have studied the role of porosity on the stiffness and stability of the surface of C-S-H gel. Our results show that 20% of gel porosity makes C-S-H in a stable phase with a lower energy and in a maximum of stiffness. We have observed that C-S-H becomes ductile when porosity is between 12.4% and 27%. Exploring the (001) surface of C-S-H informs us that more porosity and more H2O molecules on the surface makes the nanostructure thermodynamically stable.

CaCO3

C-S-H
(e)

C-S-H: Role of Porosity on the stiffness and stability of the nanogranular C-S-H gel

Recently, we have investigated a nanoscale study of the reinforcement of cement with calcite system. Our results show an increase in the elastic modulus (Young's modulus) from 21 GPa to 193 GPa, when C-S-H with 30% of gel porosity is interfaced with the (104) surface of calcite.

a) Coloidal model II. (b) Atomistic structure of a nanoparticle of C-S-H

Variation of indentation modulus with porosity compared to experiment

4. Bending and wetting of Clays: Water, contaminants and heating effects

Bending of clays

The DFT-based calculations were performed on the stripe models of the single kaolinite layer. The calculations helped to explain why halloysite mineral, a member of the kaolinite group existing in a tubular form, has rolled tubes only in one way. In that form, octahedral sheet represents the inner surface of the nanotubes. The bending models with the inner surface formed by the tetrahedral sheet showed significant structural instability with monotonically increasing strain energy as a function of the curvature. In opposite, for the bending models with the octahedral sheet as the inner surface, stabilization energetic minima were found at curvatures of about 10 nm. The calculations were also performed on the individual sheets (tetrahedral and octahedral) of the kaolinite layer to show their contribution to the bending strain. We found that the decrease of the bending energy and the layer stabilization with respect to the planar configuration for curvatures with radii RC> ~5 nm can be attributed mainly to three factors – i) better match between octahedral and tetrahedral sheets, ii) local structural changes of the SiO and AlOH polyhedral units, and iii) increasing effectivity of hydrogen bonding of outer surface OH groups.

Sketch of bending of clay

Wetting of clays

Regarding the hydrophilic behavior of clays, we have studied the wetting of Na-Montmorillonite (001) surface. The equilibrium of the water nanodroplet on Na-montmorillonite (001) surface (Figure 4) have been investigated here through Monte Carlo and Molecular dynamics simulation. The contact angle is found to be about 24° to 27° for water/Na+Mt. We have shown that the surface charge of clay mineral has great influence on the contact angle of water and clay mineral. The greater is the negative surface charge, the less is the contact angle, less is swelling behavior as well. We have previously studied the wetting behavior of KCl compound using molecular dynamics method.

Snapshots of nanodroplet of 500 TIP4P water molecules on the Na-Montmorillonite clay (001) plane with different views: front view of initial state; front view after equilibration of 1 ns; the same front view to show the distribution of Na+; top view after equilibration of 1 ns, the size of the surface (001) is 126.72 × 146.24 (Å²); front view of the profile of the zones indicated previously.

Sweling and shrinking of clays

Regarding the clays systems, our most important contributions have been related to the study of swelling and shrinking behavior of hydrated montmorillonite with different counterions (including Li+, Na+, K+, Rb+, Cs+, Ca2+, Ni2+, Zn2+, and Pb2+); under temperature effect; the study of the diffusive transport properties of water and counterions in hydrated montmorillonite, and more recently molecular dynamics study of the interactions of clay pieces under various contact have been studied. Ab initio calculations have been devoted to study the effects of divalent cations (Mg2+/Ca2+/Sr2+/Ba2+) on the structural and mechanical elasticity of montmorillonite under different degrees of hydration.

Snapshots of Ba-montmorillonite : one-layer hydrate , 4 adsorbed water molecules; one-layer hydrate, 6 water molecules; two layer hydrate, 6 water molecules

5. Clays and future of radioactive waste storage

Can clays ensure nuclear waste repositories ?

In a recent grant funded by ANDRA, we have used the nanoscale tools to analyse the disturbed zone at the atomic level in order to see the different processes responsible of this behaviour. As the main constituents of argillite are clay and calcite, a particular attention has been paid to the interaction between these two rocks under storage conditions. The assembly of the calcite (104) with montmorillonite (001) subject to storage conditions showed the fragility of the montmorillonite with respect to calcite, which resist to these conditions. Indeed, the assembly calcite / clay is more deformable in the direction perpendicular to the interface (z-direction), which is due to the lamellar clays structure.

Calcite/clay assembly: (a) before relaxation with the presence of water molecules at the interface, (b) Relaxed with water molecules at the interface

Clays pieces under constraints

The clay pieces are in contact with each other in different ways. We have shown that under the effect of environmental constraints, the clay layers of inclined pieces have a tendency to rotate and the angle between the pieces of clay to shrink. With the presence of water, the inclined layers of clay pieces turn in different ways.

Various pieces of clay in contact under the conditions of radioactive storage

6. Cleaning polluted air and soil from CO2 and radionuclides

Sequestration of CO2

The structure and dynamics of carbon dioxide molecules in hydrated Ca-montmorillonite is performed at nanoscale level. The swelling behaviour of hydrated Wyoming-type Montmorillonite including CO2 molecules and counterions is presented and analysed. In addition, the atom density profile, diffusion behaviors and radial distribution functions of CO2, interlayer water molecules and Calcium ions have been investigated at different geological burial depth of 0 km, 3 km and 6 km, which correspond to various temperature and pressure of simulation conditions. Furthermore, the influence of different hydration state on the dynamical behaviours of carbon dioxide is also explained. The calculated self-diffusion coefficient reflects that the carbon dioxide species diffuse more freely with the increase of depth and water content. The presence of interlayer CO2 inhibits the diffusion of all the mobile species. These results mainly show that the hydrated clay system is an appropriate space capable of absorbing CO2 molecules.

Relaxed structure of dehydrate, monolayer hydrate, two-layer hydrate and three-layer hydrate Ca-Wyoming montmorillonite with sequestrated CO2

Density profiles for water molecules as a function of distance from mid plane of solid layer at different burial depths for one-, two- and (c) three layer hydrates

Mineralization of CO2

We perform here a theoretical study based on both Monte Carlo and Molecular dynamic simulations in order to investigate CO2 mineral carbonation in hydrated calcium montmorillonite (Ca-MMT). Thermodynamical, structural and dynamical properties have been evaluated in order to understand the mineral carbonation characteristics of CO2 in Ca-MMT. To simulate the behavior of CO2 through mineral carbonation we consider calcium montmorillonite clays at equilibrium with H2O-CO2-H3O+-CO32- mixture under different hydration and different CO32- concentration. Radial distribution functions results indicate that average calcium-oxygen (CO32-) distance is about 2.275 Å, which is rather short because of the charge attraction. These carbonation reactions produce the stable limestone. The carbonation energy for different CO32- concentrations is calculated at different temperatures varying from 280K to 460K, gradually with 20K. The calculated diffusion coefficient indicates that the diffusion of calcium ions decreases with CO32- concentrations. Finally, the obtained mineralization energy was found in increase with carbonate concentration and burial depth.

Unrelaxed and relaxed two-layer hydrate system with 9 carbonate ions

Variation of the energy of mineralization as function of temperature

Radionuclide and soils

We have investigated the adsorption of radionuclide elements species onto substituted Montmorillonite (001) surface in the presence of different counterions. The structure and the dynamics of uranyl ion as well as its aquo, chloride ion, and carbonate complexes are analyzed. In addition, we have also studied the surface energy between layered Montmorillonite sheets and work of adhesion between radionuclide and charged Montmorillonite. The clay model used here is a Wyoming-type Montmorillonite with 0.75e negative charge per unit cell resulting from substitutions in Octahedral and Tetrahedral sheets. The system model was constructed based on CLAYFF force field potential model. To evaluate the thermodynamic work of adhesion, each surface and clay layer regions are converted to a thin film model. One and two species of radionuclide elements (UO2(H2O)5, UO2CO3(H2O)5, and UO2Cl2(H2O)5) were deposited near the clay surface in a pseudo-two-dimensional periodic cell. Analysis shows that the uranyl ion structure is preserved with two axial oxygen atoms detected at 1.8 Å. Radial distribution functions results indicate that average U-O distances are 2.45-2.61 Å for water molecules, and 2.32-2.40 Å for carbonate oxygen atoms. Average U-Cl distances are 2.85-3.08 Å, which is relatively larger than that of U-O because of electrostatic factors.

Snapshot of optimized adsorption structure of one (UO22+)(H20)5 molecule adsorbed (from top to bottom: two inner-sphere complex and one outer-sphere complex) on MMT (001) surface (a). as well as representative complex of two (UO22+)(H20)5 molecule adsorbed on MMT (001) surface (b)

Atomic density profiles for uranyl U and oxygen near the MMT surface of outer-sphere complex (a) and inner-sphere complex (b). Z0 refers to the Z coordinate of the nearest surface oxygen.

(a): Outer-sphere complex with the presence of only one uranyl and its vertical projection area on MMT surface; (b) bidentate inner-sphere complex with the presence of only one uranyl and its vertical projection area on MMT surface.

7. Rocks and Minerals

Calcite: morphology of the surface

We have performed a nanoscale analysis to study the structural and energetic stability of anhydrous (calcite, aragonite and Vaterite) and hydrous (monohydrocalcite and Ikaite) surfaces of calcium carbonate polymorphs. Besides, our computed equilibrium morphologies for calcite, aragonite and vaterite and ikaite crystals, obtained from the Gibbs–Wulff theorem, are very similar to those observed from electron spectroscopy.
(a) (b)

Equilibrium morphologies of Vaterite compared to SEM images

Ikaite: phase transformation

Since the discovery of ikaite (CaCO3.6H2O) in Antarctic marine sediments and east Arctic polar oceans, studying the ikaite-to-calcite phase transformation above 100 K has attracted a lot of interest, both experimentally and theoretically. Despite intensive efforts, the details of the thermal behaviour and the mechanisms of phase transformation between 4 and 80 K are not done experimentally. Scientists expect that the volume expansion coefficient differs from both gypsum and ice. To unlock the secrets of this rare and unstable mineral, we provide here a clear picture about the dynamical as well as the thermodynamic behaviour of ikaite. We show the presence of an anisotropic thermal expansion character more pronounced above T = 80 K, with the smallest relative expansion along b direction parallel to 2-fold axes. Our X-rays diffraction patterns show that the structure of ikaite changes above T = 75 K with the presence of new peaks. This behaviour is well observed while calculating the equilibrium unit-cell parameters between T = 2 K and T = 100 K. In the temperature range between T = 15 K and T = 100 K, ikaite exhibits a volume expansion coefficient larger than the one of ice (Ih).

Variation of the volume thermal expansion coefficients with temperature, compared to Ice (Ih) and other experimental measurements

Other carbonates: Strontianite

8. Self-healing of asphalt

Asphalt pavement is one of the main highway forms throughout the world. With the continuous development of the world economy, there have been tremendous numbers of vehicles passing on the pavements every day, causing significant irreversible damage to pavement. It is therefore necessary to study the self-healing of asphalt material, since it is directly relevant to its service life, where structure is one of the most important factors that affects its mechanical performance. Recent research shows that macro-scale cracking in asphalt binder may originate from its intrinsic defects at the nano-scale. Besides, Studies have shown that asphalt pavement damage phenomenon has a strong dependency upon asphalt-aggregate interfacial nature. If the bond between asphalt and aggregate is weak then the interface between asphalt and aggregate is prone to failure, which results in the early damage of pavement. Therefore, many methods were used to study the interface between asphalt and aggregate in different perspectives.

Initial crack of asphalt and evolution after insertion of nanoparticule

9. Nanocomposites

On polymer-clay nanocomposite materials, a PhD thesis was achieved using both experimental and theoretical parts in order to evaluate elastic moduli using a self-consistent approach. The last part of the thesis, focuses, at nanoscale level by means of MD simulation, on the analysis of the organically modified Montmorillonite and Polymer Clay Nanocomposites (PCNs).

Molecular models of Intercalated polymer clay nanocomposites (IPCNs) systems with 10 monomers in nylon chains. Polymer chains are represented in stick form and organic modifier chains in ball and stick form

10. Polymers: crystallization of polyethylene

The effect of structural composition and temperature on the crystallization and mechanical properties are studied in our group. Different crystallinity based on bond orientation parameter and global order parameter are calculated to fix the crystallinity during each process. The simulation boxes are stretched at different temperatures represent different polymer state (100 K: Glassy state; 250 K and 300K: Transition state and 400 K: Rubber state). Results indicate that the the exsitence of four stages of deformation before failure: linear elastic and yield followed by strain softening and strain hardening. In addition, temperature and structural composition are shown to have a strong influence on different mechanical characteristics of all considered polymer models.

Molecular structure screenshot of 3 initial structure

Stress-strain response at different directions

11. Stud of vulcanized and filled rubber: Physical and Mechanical properties at high strain rate

The object of this study is cis-Polyisoprene(cis-PI), the main component of natural rubber, which is vulcanized by adding elemental sulfur to cis-PI and vulcanizing at high temperature to obtain vulcanized rubber, and then adding different amounts of fullerenes to the vulcanized rubber at high temperature to obtain carbon black filled vulcanized rubber. The macroscopic physical and thermodynamic properties of vulcanized rubber and carbon black-filled vulcanized rubber were studied to obtain the effects of vulcanization and nanofiller on natural rubber. The attraction of fullerenes to cis-PI atoms and the aggregation configuration of cis-PI atoms around fullerenes were analyzed by introducing local number density and potential mean force (PMF) through RDF.

12.Prediction of new materials

For the minerals systems we were interested, first, to study the structural and dynamical properties of high-pressure phases in calcium carbonate rock, witherite and dolomite. A great contribution of atomistic simulation calculations to experimental multicyclic indentation measurements has been achieved recently. Other contributions were devoted to the prediction of new materials for civil engineering applications. The latest were based on ab initio approach and USPEX method.
Materials for civil engineering applications: Lime (CaO)

Lime system has a chemical composition CaO, which is known as thermodynamically stable. The purpose here is to explore further possible phases under pressure, by means of variable-composition ab initio evolutionary algorithm. The present investigation shows surprisingly new stable compounds of lime. At ambient pressure we predict, in addition to CaO, CaO2 as new thermodynamically stable compound. The latter goes through a phase transition from C2/c space group structure to I4/mcm space group structure at 18.5GPa. Under increasing pressure, further compounds such as CaO3 become the most stable and stabilize in P-421m space group structure above 65 GPa. For the necessary knowledge on the new predicted compounds, we have computed their mechanical and electronic properties in order to show and to explain the main reasons leading to the structural changes.

Convex hull diagrams for the Ca – O system at different pressure: (a) 1atm; (b) 50 GPa, (c) 70 GPa and (d) 100 GPa

Smithsonite

The objective here is to spread out in detail the various fundamental state properties of smithsonite rock (ZnCO3) for which the most intrinsic quantities remain still unknown. First-principles electronic structure calculations based on the density functional theory with the pseudopotential method were performed using divers functionals. A number of mechanical quantities were evaluated such as bulk modulus, elastic constants, Young and shear moduli, and transversal and longitudinal sound velocities (VS and VP). Fitting the compression data of smithsonite to the third-order Birch-Murnaghan equation of state gives a bulk modulus of 124.17 GPa, which reflects an important rigidity compared to the other carbonates. The analysis of the band structure reveals a band-gap energy of 3.36 eV that is close enough to some semiconductors rather than insulators. Finally the chemical bonding was analyzed through the electronic charge density of the total contributions of the valence bands. A pronounced charge transfer was observed towards the carbonate ion, indicating thereby the ionic character of ZnCO3.

Competitive low-energy ZnCO3 structure: a) P-31C; b) P3; c) R-3c (Phase I); d) PBCM; e) P212121(Phase III); f) PCA21; g) Pnma; h) Pna21; i) C2/m (Phase II); j) P21

Charge density in Smithsonite rock along the main planes

Oxides

The high-pressure stability of zinc oxide has been investigated here using a variable composition ab initio evolutionary algorithm. In addition to the well-known ZnO, we predict a new stable compound ZnO2 with I4/mcm space group, which becomes thermodynamically stable only above 120 GPa. Furthermore, to shed light on the new predicted compound, we have evaluated its entire ground state properties including structural, mechanical and electronic quantities. The high-pressure investigation of Zn-O shows that ZnO knows a phase transition at around 10 GPa. It stabilizes in B4 wurtzite structure at ambient conditions up to 10 GPa. Above this pressure, ZnO stabilizes in B1 structure. This agrees well with the previous experimental and theoretical studies.

Convex hull diagrams for the Zn – O system at different pressures

Enthalpies of formation of stable zinc oxides as function of pressures

Ultra-hard materials

The long search of new materials possessing exceptional properties, such as hardness continues to be a main challenge in materials science. Here we probe the ternary transition metals-nitride Ta-Mo-N system at ambient conditions by first-principles evolutionary technique in the hope of discovering new stable hard compound. A thermodynamically tetragonal stable phase Ta2Mo2N2, space group P4-nmm has been identified. Phonon dispersion and elastic constants calculations divulge the mechanical and dynamical stability of this compound. In addition, TaMoN compound shows -through electronic band structure and density of states calculations- metallic features. The hardness of Ta-Mo-N system is mainly due to the highly directional covalent Ta-N bonds.

Ternary systems

The ternary III-Nitride AlxGa1-xN ternary is one of the paradigm materials that have recently revolutionized lighting technology in the ultraviolet spectrum. A systematic investigation of the GaN-AlN system using ab initio evolutionary algorithm evidence that AlxGa1-xN alloys exist in ordered ground-state structure at ambient conditions. Cubic (AlGa3N4 (x=0.25), Al3GaN4(x=0.75)) and tetragonal (AlGaN2 (x=0.5)) are found thermodynamically quite or nearly stable. Computed elastic constants and phonons show that these phases are mechanically and dynamically stable. Using state-of-the-art LDA-1/2 approach we determine the direct band gap bowing of AlGaN alloys. We found a downward bowing parameter of b1.39eV over the entire composition range. Furthermore the optical band gap bowing is found composition-dependent. For x = 0.5, our theoretical analysis divulges that chemical effects are the main factor leading to b parameter.

13.Other topics (nanoindentation, spintronics, semiconductors, magnetic materials, metal/ceramics, energetic materials, superheating-freezing,..)

Magnetic materials and spintronics applications

Elements, binary and ternary systems

The 3D Fermi surface sheets of Polonium of first, second and third band

Electronic and optical properties of ZnSexTe(1-x)

Metal/ceramics interfaces

Energetic stabilities and bonding mechanism in Pd(111)/ZnO{0001} interfaces

Charge density at Pd/ZnO interfaces

Nanoindentation technique: case of carbide interfaces

The hardness could be evaluated, from loading and unloading process, as: H = (k.P3)/(9.W2)