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International audience; We report the results of Born-Oppenheimer molecular dynamics (BOMD) simulations on the aqueous solvation of the SmI3 molecule and of the bare Sm3+ cation at room temperature using the cluster microsolvation approach including 37 and 29 water molecules, respectively. The electronic structure calculations were done using the M062X hybrid exchange-correlation functional in conjunction with the 6-31G** basis sets for oxygen and hydrogen. For the iodine and samarium atoms, the Stuttgart-Koln relativistic effective-core potentials were utilized with their associated valence basis sets. When SmI3 is embedded in the microsolvation environment, we find that substitution of the iodine ions by water molecules around Sm(III) cannot be achieved due to an insufficient number of explicit water molecules to fully solvate the four separate metal and halogen ions. Therefore, we studied the solvation dynamics of the bare Sm3+ cation with a 29-water molecule model cluster. Through the Sm-O radial distribution function and the evolution of the Sm-O distances, the present study yields a very tightly bound first rigid Sm(III) solvation shell from 2.3 to 2.9 angstrom whose integration leads to a coordination number of 9 water molecules and a second softer solvation sphere from 3.9 to 5 angstrom with 12 water molecules. No water exchange processes were found. The theoretical EXAFS spectrum is in excellent agreement with the experimental spectrum for Sm(III) in liquid water. The strong differences between the solvation patterns of Sm(III) vs Sm(II) are discussed in detail.

International audience; Quantum-mechanical calculations are performed to investigate the structural, electronic, and infrared (IR) and Raman spectroscopic features of one of the most common radiation-induced defects in diamond: the “dumb-bell” 〈100〉 split self-interstitial. A periodic super-cell approach is used in combination with all-electron basis sets and hybrid functionals of density-functional-theory (DFT), which include a fraction of exact non-local exchange and are known to provide a correct description of the electronic spin localization at the defect, at variance with simpler formulations of the DFT. The effects of both defect concentration and spin state are explicitly addressed. Geometrical constraints are found to prevent the formation of a double bond between the two three-fold coordinated carbon atoms. In contrast, two unpaired electrons are fully localized on each of the carbon atoms involved in the defect. The open-shell singlet state is slightly more stable than the triplet (the energy difference being just 30 meV, as the unpaired electrons occupy orthogonal orbitals) while the closed-shell solution is less stable by about 1.55 eV. The formation energy of the defect from pristine diamond is about 12 eV. The Raman spectrum presents only two peaks of low intensity at wave-numbers higher than the pristine diamond peak (characterized by normal modes extremely localized on the defect), whose positions strongly depend on defect concentration as they blue shift up to 1550 and 1927 cm−1 at infinite defect dilution. The first of these peaks, also IR active, is characterized by a very high IR intensity, and might then be related to the strong experimental feature of the IR spectrum occurring at 1570 cm−1. A second very intense IR peak appears at about 500 cm−1, which, despite being originated from a “wagging” motion of the self-interstitial defect, exhibits a more collective, less localized character.

A kinetic and thermodynamic model of the Soai reaction is presented. It allows the quantitative determination of five rates constants and one equilibrium-constant. The model is realistic as it integrates the results of the most recently published X-ray structural data and DFT calculations and selected experimental kinetic data. Equipped with the extracted parameters from the numerical fitting of the time-evolution of both the substrate concentration and the enantiomeric excess, the model was able to mimic strong asymmetric amplification from extremely low initial enantiomeric excess and spontaneous mirror-image symmetry breaking from "zero catalyst" conditions. It also reproduces the crystallization conditions by exhibiting the preferential accumulation of the corresponding oligomeric species in solution. An important point is also illustrated: the autocatalytic asymmetric amplification is not located on the expected easily detectable dimers, but on the less concentrated tetrameric species.

International audience; We address the aqueous microsolvation of the CH3HgCl and CH3HgOH molecules using a stepwise hydration scheme including up to 33 water molecules and compare our results with the previously studied HgCl2, HgClOH, and Hg(OH)(2) complexes. Optimized geometries and Gibbs free energies were obtained at the B3PW91/aug-RECP(Hg)-6-31G(d,p) level. At least 33 water molecules were required to build the first solvation shell around both methylmercury compounds. Optimized geometries were found having favorable interactions of water molecules with Hg, Cl, and the OH moiety. Born-Oppenheimer molecular dynamics simulations were performed on the largest CH3HgX (X = Cl, OH)-(H2O)(33) clusters at the same level of theory. Born-Oppenheimer molecular dynamics simulations at T = 300 K (ca. 0.62 kcal/mol) revealed the presence of configurations with hydrogenbonded networks that include the OH moiety in CH3HgOH and exclude both the Hg and Cl in CH3HgCl, favoring a clathrate-type structure around the methyl moiety. The comparison to the microsolvated HgClOH, Hg(OH)(2), and HgCl2 molecules showed that, in all cases, the water molecules easily move away from Cl, thus supporting the idea that HgCl2 behaves as a non-polar solute. The theoretical (LIII edge) X-ray absorption near edge structure spectra are obtained and found in good agreement with experimental data, especially for the CH3HgCl species. Published by AIP Publishing.

International audience; The latest release of the Crystal program for solid-state quantum-mechanical ab initio simulations is presented. The program adopts atom-centered Gaussian-type functions as a basis set, which makes it possible to perform all-electron as well as pseudopotential calculations. Systems of any periodicity can be treated at the same level of accuracy (from 0D molecules, clusters and nanocrystals, to 1D polymers, helices, nanorods, and nanotubes, to 2D monolayers and slab models for surfaces, to actual 3D bulk crystals), without any artificial repetition along nonperiodic directions for 0–2D systems. Density functional theory calculations can be performed with a variety of functionals belonging to several classes: local-density (LDA), generalized-gradient (GGA), meta-GGA, global hybrid, range-separated hybrid, and self-consistent system-specific hybrid. In particular, hybrid functionals can be used at a modest computational cost, comparable to that of pure LDA and GGA formulations, because of the efficient implementation of exact nonlocal Fock exchange. Both translational and point-symmetry features are fully exploited at all steps of the calculation, thus drastically reducing the corresponding computational cost. The various properties computed encompass electronic structure (including magnetic spin-polarized open-shell systems, electron density analysis), geometry (including full or constrained optimization, transition-state search), vibrational properties (frequencies, infrared and Raman intensities, phonon density of states), thermal properties (quasi-harmonic approximation), linear and nonlinear optical properties (static and dynamic [hyper]polarizabilities), strain properties (elasticity, piezoelectricity, photoelasticity), electron transport properties (Boltzmann, transport across nanojunctions), as well as X-ray and inelastic neutron spectra. The program is distributed in serial, parallel, and massively parallel versions. In this paper, the original developments that have been devised and implemented in the last 4 years (since the distribution of the previous public version, Crystal14, occurred in December 2013) are described.

International audience; The reactivities of tris(benzyldimethylsilyl)phosphine [P(o-C6H4-CH2SiMe2H)3] (1) and tris(benzyldiphenylsilyl)phosphine [P(o-C6H4-CH2SiPh2H)3] (6) toward the same platinum precursor [Pt(PPh3)3] are strikingly different. The reaction with 1 renders the trans disilyl platinum(II) complex [PtP(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)PPh3] (2) in which the ligand coordinates in a tridentate fashion while a new Si–C bond is formed from the third Si moiety. The most prominent feature is an anagostic interaction that is established at the apical position. In contrast, the reaction of [Pt(PPh3)3] with 6 yields the hexacoordinated hydrido trisilyl platinum(IV) complex [PtHP(o-C6H4-CH2SiPh2)3PPh3] (7). We have studied the effect of the variation of the monodentate ligand in 2 by simple substitution reactions. We found a systematic variation of the chemical shift of the anagostic hydrogen in the 1H nuclear magnetic resonance spectrum of the corresponding PMe3, P(OPh)3, and CO complexes that can in principle be ascribed to a varying degree of the π acceptor character of the ancillary ligand. However, theoretical calculations at the density functional theory level show only slight changes in the frontier orbitals in line with predominantly closed-shell electrostatic interactions.

International audience; By using two different multidentate phosphinosilyl ligands, we prepared the two platinum complexes [PtPhP((o-C6H4)CH2SiMe2)2PPh3] (3) and [PtP((o-C6H4)CH2SiMe2)2(o-C6H4)CHSiMe2)PPh3] (4) exhibiting a trans configuration of the silicon atoms in a typical square-planar geometry around a Pt(II) center. Complex 4 results from intramolecular C–H activation of a methylene moiety by the third silicon atom of the original ligand and displays an anagostic C–H···Pt interaction, as supported by solution NMR data and solid-state X-ray diffraction analysis. The reactivity of 3 toward small molecules is also discussed. In the case of H2 and CO, the corresponding dihydride [PtH2PhP((o-C6H4)CH2SiMe2)2PPh3] (5) and dicarbonyl [PtPhP((o-C6H4)CH2SiMe2)2(CO)2] (6) complexes were characterized, whereas reduction to Pt(0) and release of PPh3 and HSiMe3 were observed upon thermolysis in the presence of HBpin.

International audience; Caesalpinia coriaria (C. coriaria), also named cascalote, has been known traditionally in México for having cicatrizing and inflammatory properties. Phytochemical reports on Caesalpinia species have identified a high content of phenolic compounds and shown antineoplastic effects against cancer cells. The aim of this study was to isolate and identify the active compounds of a water:acetone:ethanol (WAE) extract of C. coriaria pods and characterize their cytotoxic effect and cell death induction in different cancer cell lines. The compounds isolated and identified by chromatography and spectroscopic analysis were stigmasterol, ethyl gallate and gallic acid. Cytotoxic assays on cancer cells showed different ranges of activities. A differential effect on cell cycle progression was observed by flow cytometry. In particular, ethyl gallate and tannic acid induced G2/M phase cell cycle arrest and showed interesting effect on microtubule stabilization in Hep3B cells observed by immunofluorescence. The induction of apoptosis was characterized by morphological characteristic changes, and was supported by increases in the ratio of Bax/Bcl-2 expression and activation of caspase 3/7. This work constitutes the first phytochemical and cytotoxic study of C. coriaria and showed the action of its phenolic constituents on cell cycle, cell death and microtubules organization.

International audience; The double defect in diamond, vacancy (V) plus 100 self split-interstitial (V+I), is investigated at the ab initio quantum mechanical level, by considering the vicinal case VI1 (V is one of the first neighbors of one of the two C atoms constituting the I defect), and the two possible " second neighbors " cases, VI D 2 , VI S 2 , in which a carbon atom is a first neighbor of both V and I. The case in which the two defects are at a larger distance is simulated by considering the two isolated defects separately (VI∞). A 6-21G local gaussian-type basis set and the B3LYP hybrid functional are used for most of the calculations; richer basis sets and other functionals (a global hybrid as PBE0, a range-separated hybrid as HSE06, LDA, PBE and Hartree-Fock) have also been used for comparison. With this computational approach we evaluate the energy difference between the various spin states, the location of the corresponding bands in the energy gap of pristine diamond, as well as the defect formation energy of the four defects. The path for the recombination of V and I is explored for the vicinal case, by using the Distinguished Reaction Coordinate strategy. A barrier as high as 0.75 eV is found with B3LYP between VI1 and the perfect diamond recombined structure; when other hybrids are used, as PBE0 or HSE06, the barrier increases up to 1.01 eV (pure DFT produces lower barriers: 0.62 and 0.67 for PBE and LDA, respectively). Such a barrier is lower than the one estimated in a very indirect way through experimental data, ranging from 1.3 to 1.7 eV. It confirms however the evidence of the extremely low recombination rate also at high temperature. The Raman (and IR) spectra of the various defects are generated, that permit to attribute unambiguously (thanks also to the graphical animation of the modes) many of the peaks observed in damaged diamond above the dominant peak of perfect bulk. For the residual non attributed peaks more complicated aggregations of defects should be explored.

International audience; he structural, electronic, dielectric, and elastic properties of zigzag and armchair single-walled carbon nano- tubes are investigated at different DFT levels (LDA, GGA, hybrids) with Gaussian type basis sets of increasing size (from 3-21G to 6-1111G(2d,f)). The longitudinal and transverse polarizabilities are evaluated by using the Coupled Perturbed Hartree-Fock and Kohn-Sham computational schemes, which take into account the orbital relaxation through a self- consistent scheme. It is shown that the difference between the frequently adopted SOS (sum over states, uncoupled) and the fully coupled results is far from being negligible and varies as a function of the tensor component and the adopted functional. Helical symmetry is fully exploited. This allows simulation of tubes larger (up to 140 atoms in the unit cell) than in previous studies by using extended basis sets and severe computational conditions. All the 12 functionals considered here provide similar results for the structural and the elastic properties and for the relative stability among nanotubes and with respect to graphene. On the contrary, the stability with respect to diamond, which has a quite different density than that of nanotubes, sensitively depends on the adopted functional. The band gap and the longitudinal polarizability are strongly dependent on the level of approximation: hybrid functionals provide the least deviation from experimental data. In general, data obtained for (n, n), (3n, 0), (3n + 1, 0), and (3n + 2, 0) rolling directions approach the slab limit for large radii following four distinct trends.

International audience; We study the nature of the electron pairing at the most important critical points of the singlet potential energy surface of the 2O2 O4 reaction and its evolution along the reaction coordinate using the electron pair localization function (EPLF) [Scemama, A.; Chaquin, P.; Caffarel, M. J. Chem. Phys. 2004, 121, 1725]. To do that, the 3D topology of the EPLF calculated with quantum Monte Carlo (at both variational and fixed-node-diffusion Monte Carlo levels) using Hartree-Fock, multiconfigurational CASSCF, and explicitly correlated trial wave functions is analyzed. At the O4 equilibrium geometry the EPLF analysis reveals four equivalent covalent bonds and two lone pairs on each oxygen atom. Along the reaction path toward dissociation it is found that the two oxygen-oxygen bonds are not broken simultaneously but sequentially, and then the lone pairs are rearranged. In a more general perspective, the usefulness of the EPLF as a unique tool to analyze the topology of electron pairing in nontrivial chemical bonding situations as well as to visualize the major steps involved in chemical reactivity is emphasized. In contrast with most standard schemes to reveal electron localization (atoms in molecules, electron localization function, natural bond orbital, etc.), the newly introduced EPLF function gives a direct access to electron pairings in molecules.

International audience; Treatment of 5-formyl-2-furanboronic acid with 2-aminophenol 4,5-(R) substituted (R = -Cl, -NO2, -CH3, -CO2H, naphtyl) offers bicyclic boronates, in which a furan ring-opening reaction is involved. Even though the reaction proceeds in all cases, lower yields were obtained when aminophenol derivatives include electron withdrawing substituents. Evaluation of the photophysical properties for all compounds showed substantial solvatochromic and luminescent changes. The solvatochromic effect was clear noticed from changes in color solutions from solvents with different polarities/polarizabilities and hydrogen bonding capacities. Influence of the substituents is also appreciable at the absorption and emission spectra, in where the nitro derivatives showed poor absorbance and emission bands. In addition, computational NLO properties were calculated which showed beta values from 29 to 139 x 10(-30) cm(5) esu(-1), showing thus possible applications as optoelectronic materials.

The evolution under pressures up to 65 GPa of structural, elastic and vibrational properties of the katoite hydrogarnet, Ca3Al2(OH)12, is investigated with an ab initio simulation performed at the B3LYP level of theory, by using all-electron basis sets with the Crystal periodic program. The high-symmetry Ia3d phase of katoite, stable under ambient conditions, is shown to be destabilized, as pressure increases, by interactions involving hydrogen atoms and their neighbors which weaken the hydrogen bonding network of the structure. The corresponding thermodynamical instability is revealed by anomalous deviations from regularity of its elastic constants and by numerous imaginary phonon frequencies, up to 50 GPa. Interestingly, as pressure is further increased above 50 GPa, the Ia3d structure is shown to become stable again (all positive phonon frequencies and regular elastic constants). However, present calculations suggest that, above about 15 GPa and up to at least 65 GPa, a phase of I4[combining macron]3d symmetry (a non-centrosymmetric subgroup of Ia3d) becomes more stable than the Ia3d one, being characterized by strengthened hydrogen bonds. At low-pressures (between about 5 GPa and 15 GPa), both phases show some instabilities (more so for I4[combining macron]3d than for Ia3d), thus suggesting either the existence of a third phase or a possible phase transition of second order.

International audience; The static and high frequency dielectric tensors, Born effective charges, vibrational spectrum at the Γ point, TO-LO splitting and IR intensities of calcite CaCO3 have been calculated with the periodic ab initio CRYSTAL program, with five different basis sets of increasing size and four different Hamiltonians (HF, LDA, PBE, B3LYP). B3LYP is shown to perform better than the other options, in particular of LDA and PBE that are often used for the calculation of the vibrational spectrum of crystalline solids. When comparing B3LYP and experimental frequencies, the mean absolute difference is as small as 8.5 cm-1; this number reduces to 4.8 cm-1 if the two lowest experimental frequencies, that we suspect to be affected by a relatively large error, are excluded from statistics. Static and high frequency dielectric tensors, as well as IR intensities computed with the same hybrid scheme (B3LYP) compare quite favourably with experiment. The full set of modes is characterized by various tools including isotopic substitution, “freezing” one of the two subunits (Ca2+ or CO32-) and graphical representations. A general tool has been implemented, that permits the automatic generation of the animation of the full set of modes starting from the CRYSTAL output (available at www.crystal.unito.it/vibs/calcite).

The harmonic frequency spectrum of bulk Mg(OH)(2), brucite, has been computed with the CRYSTAL periodic code, using four different hamiltonians, namely Hartree-Fock (HF), local density (LDA), gradient corrected PW91 and hybrid B3LYP. The anharmonicity of the 011 stretching frequency has also been evaluated, as well as the transverse/longitudinal optical (TO/LO) splitting. Comparison with the frequencies of the single layer shows that the bulk OH stretching splitting is due to interlayer interaction. Agreement with experiment is excellent for B3LYP (less than 10 cm(-1) differences), less so for PW91 and much less satisfactory for both LDA and HF. (C) 2004 Elsevier B.V. All rights reserved

Electron donor–acceptor (EDA) interactions are widely involved in chemistry and their understanding is essential to design new technological applications in a variety of fields ranging from material sciences and chemical engineering to medicine. In this Letter, we study EDA complexes of carbon dioxide with ketones using several ab initio and density functional theory methods. Energy contributions to the interaction energy have been analyzed in detail using both variational and perturbational treatments. Dispersion energy has been shown to play a key role in explaining the high stability of a non-conventional structure, which can roughly be described by a cooperative EDA interaction.

International audience; Three new N-heterocyclic-silazane compounds, 1a-c, were prepared and employed as bidentate ligands to ruthenium, resulting in a series of [Ru(H){(κ-Si,N-(SiMe2-N-heterocycle)}3] complexes (3a-c) featuring the same RuSi3H motif. Detailed structural characterization of the RuSi3H complexes with X-ray diffraction, and in the case of triazabicyclo complex [Ru(H){κ-Si,N-(SiMe2)(C7H12N3)}3] (3a), neutron diffraction, enabled a reliable description of the molecular geometry. The hydride ligand of (3a) is located closer to two of the silicon atoms than it is to the third. Such a geometry differs from that of the previously reported complex [Ru(H){(κ-Si,N-(SiMe2)N(SiMe2H)(C5H4N)}3] (3d), also characterized by neutron diffraction, where the hydride was found to be equidistant from all three silicon atoms. A DFT study revealed that the symmetric and less regular isomers are essentially degenerate. Information on the dynamics and on the Ru***H***Si interactions was gained from multinuclear solid-state (1H wPMLG, 29Si CP MAS, and 2D 1H-29Si dipolar HETCOR experiments) and solution NMR studies. The corresponding intermediate complexes, [Ru{κ-Si,N-(SiMe2-N-heterocycle)}(η4-C8H12)(η3-C8H11)] (2a-c), involving a single silazane ligand were isolated and characterized by multinuclear NMR and X-ray diffraction. Protonation of the RuSi3H complexes was also studied. Reaction of 3a with NH4PF6 gave rise to [Ru(H)(η2-H −SiMe2)κ-N-(C7H12N3){κ-Si,N-(SiMe2)(C7H12N3)}2]+[PF6]−(4aPF6) which was isolated and characterized by NMR spectroscopy, X-ray crystallography, and DFT studies. The nature of the Si-H interactions in this silazane series was analyzed in detail.

International audience; The properties of the (n,n) icosahedral family of carbon fullerenes up to n = 10 (6000 atoms) have been investigated through ab initio quantum-mechanical simulation by using a Gaussian type basis set of double zeta quality with polarization functions (84,000 atomic orbitals for the largest case), the hybrid B3LYP functional and the CRYSTAL14 code featuring generalization of symmetry treatment. The geometry of giant fullerenes shows hybrid features, between a polyhedron and a sphere; as n increases, it approaches the former. Hexagon rings at face centres take a planar, graphene-like configuration; the 12 pentagon rings at vertices impose, however, a severe structural constraint to which hexagon rings at the edges must adapt smoothly, adopting a bent (rather than sharp) transversal profile and an inward longitudinal curvature. The HOMO and LUMO electronic levels, as well as the band gap, are well described using power laws. The gap is predicted to become zero for n ≥ 34 (69,360 atoms). The atomic excess energy with respect to the ideal graphene sheet goes to zero following the log(Nat)/Nat law, which is well described through the continuum elastic theory applied to graphene; the limits for the adopted model are briefly outlined. Compared to larger fullerenes of the series, C60 shows unique features with respect to all the considered properties; C240 presents minor structural and energetic peculiarities, too.

The capabilities of the CRYSTAL14 program are presented, and the improvements made with respect to the previous CRYSTAL09 version discussed. CRYSTAL14 is an ab initio code that uses a Gaussian-type basis set: both pseudopotential and all-electron strategies are permitted; the latter is not much more expensive than the former up to the first-second transition metal rows of the periodic table. A variety of density functionals is available, including as an extreme case Hartree-Fock; hybrids of various nature (global, range-separated, double) can be used. In particular, a very efficient implementation of global hybrids, such as popular B3LYP and PBE0 prescriptions, allows for such calculations to be performed at relatively low computational cost. The program can treat on the same grounds zero-dimensional (molecules), one-dimensional (polymers), two-dimensional (slabs), as well as three-dimensional (3D; crystals) systems. No spurious 3D periodicity is required for low-dimensional systems as happens when plane-waves are used as a basis set. Symmetry is fully exploited at all steps of the calculation; this permits, for example, to investigate nanotubes of increasing radius at a nearly constant cost (better than linear scaling!) or to perform self-consistent-field (SCF) calculations on fullerenes as large as (10,10), with 6000 atoms, 84,000 atomic orbitals, and 20 SCF cycles, on a single core in one day. Three versions of the code exist, serial, parallel, and massive-parallel. In the second one, the most relevant matrices are duplicated, whereas in the third one the matrices in reciprocal space are distributed for diagonalization. All the relevant vectors are now dynamically allocated and deallocated after use, making CRYSTAL14 much more agile than the previous version, in which they were statically allocated. The program now fits more easily in low-memory machines (as many supercomputers nowadays are). CRYSTAL14 can be used on parallel machines up to a high number of cores (benchmarks up to 10,240 cores are documented) with good scalability, the main limitation remaining the diagonalization step. Many tensorial properties can be evaluated in a fully automated way by using a single input keyword: elastic, piezoelectric, photoelastic, dielectric, as well as first and second hyperpolarizabilies, electric field gradients, Born tensors and so forth. Many tools permit a complete analysis of the vibrational properties of crystalline compounds. The infrared and Raman intensities are now computed analytically and related spectra can be generated. Isotopic shifts are easily evaluated, frequencies of only a fragment of a large system computed and nuclear contribution to the dielectric tensor determined. New algorithms have been devised for the investigation of solid solutions and disordered systems. The topological analysis of the electron charge density, according to the Quantum Theory of Atoms in Molecules, is now incorporated in the code via the integrated merge of the TOPOND package. Electron correlation can be evaluated at the Moller-Plesset second-order level (namely MP2) and a set of double-hybrids are presently available via the integrated merge with the CRYSCOR program. (C) 2014 Wiley Periodicals, Inc.

A comprehensive kinetic analysis of three prototypical autocatalytic cycle models based on the absolute asymmetric Soai reaction is presented. The three models, which can give rise to amplification of enantiomeric excess and mirror-image symmetry breaking, vary by their monomeric, dimeric or trimeric order of the assumed catalytic species. Our numerical approach considered the entire chiral combinatorics of the diastereomeric interactions in the models as well as the multiplicity of coupled reversible reactions without applying fast equilibration or quasi-steady state approximations. For the simplest monomeric model, an extensive range of parameters was explored employing a random grid parameter scanning method that revealed the influence of the parameter values on the product distribution, the reaction-time, the attenuation or amplification of enantiomeric excess as well as on the presence or absence of mirror-image symmetry breaking. A symmetry breaking test was imposed on the three models showing that an increase in the catalytic oligomer size from one to three leads to a higher tolerance to poorer chiral recognition between the diastereoisomers and identifies the greater impact of the diastereoisomeric energy difference over an imperfect stereoselectivity in the catalytic step. This robustness is understood as a particular case of so-called kinetic proofreading in asymmetric autocatalysis.

International audience; Aluminum hydroxides (a family of seven compounds) are key raw materials in the aluminum industry, and indeed an extremely large variety of experiments and simulations was performed in the last 50 years on this class of materials. However, many of their properties still remain a matter of debate, as a comprehensive and comparative analysis of the full family is still lacking. Some of the open questions related to their structure (space group definition, H order-disorder), energetics (relative stability with respect to each other and to the dehydrated phase), and vibrational spectrum (broad bands in the OH stretching region causing large differences in the interpretation of the experi- mental IR and Raman spectra by the various authors) are addressed in this work with a quantum mechanical ab initio approach, using the CRYSTAL09 periodic code, a rich all-electron Gaussian type basis set, and the hybrid B3LYP functional. This review presents the first complete, systematic, and homogeneous (same method, computational parameters, basis set, and Hamiltonian) investigation of the crystal structure, energetics, and vibrational spectra of this family of compounds, showing that quantum mechanical simulation is likely to provide complementary data for their complete characterization.

International audience; The vibrational spectrum of the Si-free katoite hydrogarnet (116 atoms in the unit cell) has been calculated at the periodic ab initio quantum mechanical level with the CRYSTAL program, by using a Gaussian type basis set and the hybrid B3LYP Hamiltonian. The harmonic frequencies at the Gamma point have been obtained by diagonalizing the mass-weighted Hessian matrix, that is evaluated by numerical differentiation of the analytical first derivatives of the energy with respect to the atomic Cartesian coordinates. The parameters controlling the numerical differentiation, as well as the numerical integration of the exchange-correlation functional for the self-consistent field (SCF) calculation, are shown to affect the obtained frequencies by less than 3 cm-1. Before diagonalization, the dynamical matrix is transformed to a block diagonal form according to the irreducible representations of the point group, so that the 345 vibrational modes are automatically classified by symmetry. Various tools are adopted (graphical representation, isotopic substitution, "freezing" part of the unit cell) that permit a complete classification of normal modes and, in particular, an analysis of the modes in terms of simple models (octahedra modes, Ca modes, H stretching, bending, rotations). The harmonic OH stretching band (48 modes) is quite narrow (20 cm-1), indicating that the interaction among OH groups is very weak. As the OH stretching modes are known to be totally separable from the other modes and strongly anharmonic, the one-dimensional Schroedinger equation for the anharmonic oscillator is solved numerically for the two extreme situations, corresponding to the vibration of one decoupled OH and of all 48 OH groups moving in phase. The anharmonic frequencies are 3682 and 3673 cm-1, respectively, in good agreement with IR experiments (a single band at 3661 cm-1 with a width at half band height of 33 cm-1) and confirming that the interaction between OH groups is extremely weak.

International audience; The vibrational spectrum of Mg3Al2Si3O12 pyrope is calculated at the Γ point by using the periodic ab initio CRYSTAL program that adopts an all-electron Gaussian-type basis set and the B3LYP Hamiltonian. The full set of frequencies (17 IR active, 25 RAMAN active, 55 silent modes) is calculated. The effect of the basis set and of the computational parameters on the calculated frequencies is discussed. It is shown that the mean absolute difference with respect to the experimental IR and RAMAN data is as small as 6 and 8 cm-1, respectively. The IR and RAMAN modes are fully characterized by various tools such as isotopic substitution, direct inspection of the eigenvectors, and graphical representation. The present calculation permits to clarify some of the assignment and interpretation problems raised by experiment and previous simulations with force fields.

The determination of the solvation shell of Hg(II)-containing molecules and especially the interaction between Hg(II) and water molecules is the first requirement to understand the transmembrane passage of Hg into the cell. We report a systematic DFT study by stepwise solvation of HgCl(2) including up to 24 water molecules. In order to include pH and salinity effects, the solvation patterns of HgClOH, Hg(OH)(2) and HgCl(3)(-) were also studied using 24 water molecules. In all cases the hydrogen bond network is crucial to allow orbital-driven interactions between Hg(II) and the water molecules. DFT Born-Oppenheimer molecular dynamics simulations starting from the stable HgCl(2)-(H(2)O)(24) structure revealed that an HgCl(2)-(H(2)O)(3) trigonal bipyramid effective solute appears and then the remaining 21 water molecules build a complete first solvation shell, in the form of a water-clathrate. In the HgCl(2), HgClOH, Hg(OH)(2)-(H(2)O)(24) optimized structures Hg also directly interacts with 3 water molecules from an orbital point of view (three Hg-O donor-acceptor type bonds). All the other interactions are through hydrogen bonding. The cluster-derived solvation energies of HgCl(2), HgClOH and Hg(OH)(2) are estimated to be -34.4, -40.1 and -47.2 kcal mol(-1), respectively.