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Dans le cadre d’un dispositif d’évaluation formative et précoce des prérequis à l’entrée des études universitaires, des étudiants de première année ont été amenés à s’auto-évaluer en estimant leur degré de maîtrise de chacun des prérequis testés sur une échelle de trois niveaux spécifiés au préalable. S’inscrivant dans la perspective du feedback « durable », l’auto-évaluation a été introduite dans le dispositif, car elle constitue une étape importante dans un processus visant à développer l’autonomie de l’étudiant, indispensable à sa réussite dans l’enseignement supérieur. Dans ce processus d’auto-évaluation, l’étudiant a d’abord été amené à poser un auto-diagnostic lors de la présentation d’un « Passeport », ce diagnostic étant censé amener l’étudiant à entamer une démarche de régulation par sa participation à des activités de renforcement. Dans cet article, le niveau d’exactitude du comportement d’auto-évaluation des étudiants est d’abord étudié. Les facteurs associés au comportement d’auto-évaluation sont ensuite analysés, en examinant notamment le genre (garçon-fille), le niveau de maîtrise réelle des prérequis, ainsi que la participation aux activités de renforcement. Nous analysons enfin les représentations des étudiants de l’activité même d’auto-évaluation. L’article se termine par une discussion sur les limites de la recherche et par des propositions d’implications pédagogiques. Within the context of an early and formative evaluation framework assessing prerequisites when entering university, first-year students were asked to practice self-assessment by estimating their degree of mastery of each assessed prerequisite on a three-level scale specified beforehand. With a view to a « sustainable » feedback, self-assessment has been introduced within this framework, since it represents a major step in a process aiming at developing student autonomy, which is essential to succeed in higher education. To start this self-assessment process, students had to take a so-called « Passport » and make a self-diagnosis. The latter is intended to bring students to enter a regulation process through their taking part to capacity-building activities. In this paper, we will first study the accuracy level of student self-assessment behaviour. Factors associated to this behaviour will be then analyzed, taking special attention to students’ gender (male/female), their real degree of mastery of prerequisites, as well as their taking part to capacity-building activities. Finally, we will analyze how students perceive the self-assessment activity itself. The article ends with a discussion on the limits of this research and some proposals of educational implications.

Using the parameter-free PBE0 hybrid functional in conjunction with the conducting PCM model, we compute the UV/VIS spectra of a series of solvated phenol and nitrobenzene chromogens. For the first series, the average deviation with respect to experiment is large (about 0.5 eV) but the auxochromic shifts are very accurately and consistently predicted. Therefore, after a statistical treatment, the TD-DFT values are within 0.02 eV of the experimental data. For nitrobenzenes, the average discrepancy is smaller than for phenols, though the impact of individual substitution is much less consistent with experimental trends. We also confirm that push-pull compounds with donor and acceptor groups in meta positions are especially problematic for TD-DFT calculations relying on conventional hybrids, and we unravel the origin of this specific difficulty.

Using a state-of-the-art time-dependent density functional (TD-DFT) approach that includes the explicit consideration of bulk medium effects on both the ground-state geometry and the electronic spectrum, we have determined the λmax of 86 naphthoquinones (NQ) dyes in various solvents for a total of 151 cases. In most cases, TD-DFT provides the correct ordering of transitions for substituted NQ dyes. Comparisons with experimental values lead to a mean signed error of −7.2 nm (0.039 eV) and a mean absolute error of 20.1 nm (0.113 eV). It turns out that the average errors are smaller for the hydroxy and methoxy derivatives, than for amino substituted dyes. It is also demonstrated that the statistical treatment of the data does not significantly improve the agreement between the experimental and the theoretical values. We also discuss average basis set effects and solvatochromism.

The UV/vis absorption spectra of 101 anthraquinones solvated in two protic solvents (methanol and ethanol) has been theoretically predicted using the time-dependent density functional theory (TD-DFT) for the excited state calculations and the polarizable continuum model (PCM) for evaluating bulk solvent effects. Two functionals (B3LYP and PBE0) have been used and they provide similar mean absolute deviations (approximately 0.09 eV) but mean signed errors presenting opposite signs. The errors can be minimized by using simple or multiple linear regression, the latter combining the results of both functionals to reach an optimal estimation of the lambda(max) (mean absolute error 0.06 eV). Specific fittings for the two media have been performed and it turned out that our approach is even more efficient for anthraquinones solvated in ethanol.

The absorption spectra of a large panel of substituted arylcarbonium dyes have been simulated with the PCM-TD-DFT theoretical scheme. For most compounds, there are at least two allowed excited-states showing a strong molar absorption coefficient in the UV/Vis region. Both involve a charge transfer from the para-NMe2 to the central carbonium. It turns out that B3LYP, combined with the 6-31G(d,p) basis set for the ground-state optimization, and with the 6-311G(d,p) basis set for the TD-PBE0 calculations, yields reliable auxochromic shifts when the solvation effects are included in the model. Indeed, a statistical treatment of the raw TD-DFT results allows a prediction of the λmax with a small average standard deviation: 26 nm. The accuracy required for the design of new molecules is globally reached: the mean average error is only 19 nm, in spite of the charge-transfer nature of the excitations. Moreover, linear correlations have been established between: (i) the ring-N average bond length and the experimental λ max ( 1 - 2 ) , (ii) vibrational frequency of the chromophore and the λ max ( 2 ) .

Extensive Time-Dependent Density Functional Theory (TD-DFT) calculations have been carried out in order to obtain a statistically meaningful analysis of the merits of a large number of functionals. To reach this goal, a very extended set of molecules (∼500 compounds, >700 excited states) covering a broad range of (bio)organic molecules and dyes have been investigated. Likewise, 29 functionals including LDA, GGA, meta-GGA, global hybrids, and long-range-corrected hybrids have been considered. Comparisons with both theoretical references and experimental measurements have been carried out. On average, the functionals providing the best match with reference data are, one the one hand, global hybrids containing between 22% and 25% of exact exchange (X3LYP, B98, PBE0, and mPW1PW91) and, on the other hand, a long-range-corrected hybrid with a less-rapidly increasing HF ratio, namely LC-ωPBE(20). Pure functionals tend to be less consistent, whereas functionals incorporating a larger fraction of exact exchange tend to underestimate significantly the transition energies. For most treated cases, the M05 and CAM-B3LYP schemes deliver fairly small deviations but do not outperform standard hybrids such as X3LYP or PBE0, at least within the vertical approximation. With the optimal functionals, one obtains mean absolute deviations smaller than 0.25 eV, though the errors significantly depend on the subset of molecules or states considered. As an illustration, PBE0 and LC-ωPBE(20) provide a mean absolute error of only 0.14 eV for the 228 states related to neutral organic dyes but are completely off target for cyanine-like derivatives. On the basis of comparisons with theoretical estimates, it also turned out that CC2 and TD-DFT errors are of the same order of magnitude, once the above-mentioned hybrids are selected.

The electronic excited states of solvated 1,4-naphthoquinone dyes have been determined using time-dependent density functional theory (TD-DFT) combined with the polarizable continuum model (PCM). It turns out that the 6-311+G(2d,p) and 6-311G(d,p) basis sets provide, respectively, almost perfectly converged excitation spectra, and geometries. Using the PBE0 hybrid functional, we obtain a valuable correlation between PCM-TD-DFT and experimental transitions in both the ultraviolet and the visible parts of the absorption spectra. Indeed, for the 69 1,4-naphthoquinone studied transitions, the mean signed/absolute deviation are limited to +3.6 nm (−0.048 eV)/9.5 nm (0.100 eV). Qualitative correlations between the geometrical, vibrational and electronic characteristics has been established. In addition, the spectra of several 1,2-naphthoquinones have been considered.

The UV absorption spectra of more than 80 substituted coumarins and chromones have been investigated with the PCM-TD-DFT theoretical scheme using three hybrid functionals (O3LYP, B3LYP, and PBE0) and taking into account methanol or ethanol solvation effects. For most of the studied derivatives, there are at least two allowed excited states presenting a strong oscillator strength in the UV region. The first allowed excitation is associated to a HOMO-LUMO transition whereas the second corresponds to a transition from the HOMO-1 to the LUMO. Both involve a charge transfer from the benzenic cycle to the pyranone moiety. Statistically treating the PBE0 results allows a prediction of the lambda(max) with small standard deviations: in methanol, 6 nm (0.07 eV) for the first excitation (lambda(max)(1)) and 5 nm (0.08 eV) for the second one (lambda(max)(2)), whereas in ethanol 6 nm (0.08 eV) for (lambda(max)(1)) and 6 nm (0.13 eV) for (lambda(max)(2)).

The structure and visible spectra of a large panel of thioindigo dyes and derivatives have been evaluated using a TD-PBE0/6-311+G(2d,p)//PBE0/6-311G(d,p) approach explicitly taking bulk solvent effects into account by means of the polarizable continuum model. The influence of the solvent characteristics, the trans-cis isomerization, and the chemical substitution on the benzene rings have been investigated. In addition, hemi-thioindigo dyes, thiazine-indigo, chromophore-like molecules, and selenoindigo have been considered. Though the relative oscillator strengths of the two allowed visible transitions in the nonplanar cis isomers are not always correctly reproduced by theory, the agreement between theoretical and experimental results is far above expectations. For the 170 cases studied, we obtained a mean unsigned error on the predicted lambda(max) limited to 6.9 nm or 0.03 eV, with only 6 (4) cases for which the difference exceeds 20 nm (0.10 eV). These errors are 1 order of magnitude smaller than what has previously been reported for indigoids. A linear correlation between the central double bond length and the lambda(max) has been established, while the bond length and vibrational frequency of the carbonyl groups do not correlate with the thioindigo color. The higher excitation energies of the cis conformers, compared to the trans structures, result from a less stabilized LUMO in the former case. Indeed, for cis thioindigo, the two electron-rich (in the excited state) carbonyl units lie close to each other.

Using the parameter-free PBE0 hybrid functional, we compute the UV/Vis spectra of a series of solvated compounds presenting a carbonyl chromophoric unit linked to a carbon- carbon double bond. It turns out that PBE0 is extremely efficient for accurately reproducing experimental values, with a mean unsigned error of 7 nm for an extended set of compounds, although no fitting or statistical treatments are performed. PBE0 has a predictive efficiency comparable to the well-known Woodward-Fieser empirical formula, and can therefore be used to extend these rules without requiring additional experimental results. Consequently, the UV/Vis spectra of several compounds that have not yet been synthesized are predicted. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem 106: 1853-1859, 2006

The low-lying excited states of trans -thioindigo derivatives have been determined by using time-dependent density functional theory. A large panel of atomic basis sets has been tested and it turns out that 6-311G(d,p) provides accurate geometries, whereas a more extended basis, 6-311+G(2d,p), is necessary for describing excited states. Adamo and Barone's fitted-parameter-free hybrid functional (PBE0) gives λ max in very good agreement with experiment once bulk solvent effects are taken care off. Using the PCM-TD-PBE0/6-311+G(2d,p)//PCM-PBE0/6-311G(d,p) level of theory, the effects of various types of substitution are accurately reproduced; with the largest λ max deviation being limited to 10 nm.

With computational chemistry techniques explicitly taking into account electron correlation and solvatation effects, we have investigated the impact of the chemical substitution of 1,4-diNHPh-9,10-anthraquinone on its λ max of absorption in the visible spectra as well as on the corresponding oscillator strength. Although, the impact of chemical substitution on the λ max is less dramatic than for unsubstituted 9,10-anthraquinone, bathochromic (up to +120 nm) and hypsochromic shifts (up to −13 nm) as well as hyper/hypo shifts have been computed. The largest bathoshift has been observed when two (additional) hydrogen bonds are built up between the auxochromic groups and the C O chromophores.

We have investigated the structures and the properties of polyaminoborane oligomers by using ab initio computational tools including dynamic electron correlation effects. It turned out that the PBE0/6-31G(2d) method provides a good agreement between experimental and theoretical structures. The key data include geometries, rotational profiles, infrared spectra, vertical excitation energies, atomic charges, and dipole moments. The variations of these properties upon conformation changes are studied. Our results are compared to available experimental measurements.

We have investigated with computational chemistry techniques the visible spectra of substituted anthraquinones. A wide panel of theoretical methods has been used, with various basis sets and density functional theory (DFT) functionals, in order to assess a level of theory that would lead to converged excitation energies. It turns out that the hybrid Becke-Lee-Yang-Parr and Perdew-Burke-Erzenrhof functionals with the 6-31G (d,p) atomic basis set provide reliable lambda(max) when the solvent effects are included in the model. Combining the results of both DFT schemes allows the prediction of lambda(max) with a standard deviation limited to 13 nm.

The impact of side-group substitution on the three-dimensional structure and on the properties of the homologuous series of polyphosphinoborane oligomers has been investigated by using ab initio computational tools, taking into account dynamic electron correlation effects. This includes the evaluation of the following: geometries, conformations, rotational profiles, infrared spectra, vertical excitations energies, atomic charges, and dipole moments.

Using plane wave basis functions within the local density approximation, the Car-Parrinello molecular dynamics scheme has been applied to evaluate the vibrational frequencies of the H2O and CO2 molecules. This dynamical approach using the plane wave basis set provides estimates of similar quality to standard density functional schemes using gaussian basis sets.

The vibrational frequency of selected diatomic molecules (H 2 , N 2 , F 2 , HF, CO) has been calculated from Car-Parrinello molecular dynamics. The associated electronic energies have been obtained within the Born-Oppenheimer approximation by using the local density functional scheme where plane waves and pseudopotentials are used. Our vibrational frequency results, extrapolated to zero effective fictitious mass values, are in good agreement with the experimental values for H 2 , N 2 , HF and CO, whereas for F 2 our calculated value is larger. The optimized bond lengths and the harmonic vibrational frequencies obtained by a local density functional scheme with plane waves have been compared with other theoretical methods (Hartree-Fock, MP2, CCSD(T), DFT using Gaussian basis sets). There is good agreement between the LDA procedure using plane-wave or Gaussian-type orbital basis sets.

This work presents a quantitative structure–property relationship (QSPR)-based approach allowing an accurate prediction of the excited-state properties of organic dyes (anthraquinones and azobenzenes) from ground-state molecular descriptors, obtained within the (conceptual) density functional theory (DFT) framework. The ab initio computation of the descriptors was achieved at several levels of theory, so that the influence of the basis set size as well as of the modeling of environmental effects could be statistically quantified. It turns out that, for the entire data set, a statistically-robust four-variable multiple linear regression based on PCM-PBE0/6-31G calculations delivers a R adj 2 of 0.93 associated to predictive errors allowing for rapid and efficient dye design. All the selected descriptors are independent of the dye's family, an advantage over previously designed QSPR schemes. On top of that, the obtained accuracy is comparable to the one of the today's reference methods while exceeding the one of hardness-based fittings. QSPR relationships specific to both families of dyes have also been built up. This work paves the way towards reliable and computationally affordable color design for organic dyes.

A large series of photochromes of the spirooxazine family has been investigated using density functional theory and time-dependent density functional theory, aiming at designing molecules with an open-ring merocyanine form absorbing at the longest possible wavelength. A complete methodological assessment (basis set, solvent effects, functionals) has been performed, allowing the design of efficient multilinear regressions for two solvents (cyclohexane and toluene). These regressions allow the estimate of the absorption wavelength of open spirooxazine with an error limited to about 5 nm. The thermodynamic and spectral properties of several isomers have been considered, and it turned out that only TTC and CTC structures may appear experimentally. These structures present similar stabilities and absorption wavelengths. The impact of the auxochromic groups on the UV/vis spectra was assessed and novel promising substitution patterns have been unravelled. It is shown that using a strong push moiety on the same side of the molecule as the pull group may be an effective procedure for tuning the visible spectra. In particular, several spirooxazines with absorption wavelength predicted to be close to or larger than 700 nm are proposed.

La chimie industrielle du XXI e siecle se doit de relever de nombreux defis economiques et environnementaux afin d'assurer son developpement futur. Les domaines prioritaires ont trait a l'ingenierie des procedes (thermodynamique, cinetique...) et aux techniques de modelisation (chimie calculatoire, simulations de procedes, dynamique des fluides...). S'il est aujourd'hui communement admis que la chimie quantique constitue une des nombreuses facettes de la chimie physique, le chemin qui mene a la reconnaissance de sa capacite de prediction et d'interpretation de phenomenes physico-chimiques n'a pas pour autant ete un long fleuve tranquille. Loin des diatribes infondees dont elle est encore parfois la cible, la chimie calculatoire est neanmoins occupee a gagner son pari, comme en temoigne cette intervention de Gilbert Gaillard [1], ancien president de la societe francaise Hoechst: « Aujourd'hui, la chimie industrielle a sa source dans la chimie theorique dont elle est l'application, l'accomplissement, et qu'elle contribue a enrichir par les questions qu'elle lui soumet. Par ailleurs, elle met en œuvre les acquis d'autres sciences fondamentales: physique, thermodynamique, mecanique, genie des procedes... Ces apports constituent son paysage quotidien et lui assurent des possibilites de developpement ». Les methodes de chimie quantique impliquent la description mathematique d'un systeme constitue de noyaux et d'electrons, constitutifs de la matiere [2], et la resolution d'equations comme celle de Schrodinger. L'application pratique de ces techniques passe par l'elaboration et la programmation d'algorithmes permettant la description quantitative des phenomenes physiques et chimiques au sein de ce systeme. Les applications de la chimie calculatoire en matiere de genie des procedes sont nombreuses et variees: prediction de donnees spectroscopiques et thermochimiques, developpement de nouvelles molecules possedant une reactivite selective, amelioration des procedes existants et elaboration de nouveaux processus... L'exemple des equations d'etat constitue une excellente illustration de la capacite des ingenieurs chimistes a appliquer et a developper des concepts et des modeles originellement concus par les theoriciens. Cette tendance se precise avec l'avenement et la vulgarisation des equations d'etat non cubiques [3] qui s'imposent avec force au niveau industriel. Les proprietes calculees au niveau quantique peuvent etre utilisees comme variable d'essai pour un traitement posterieur, contribuant ainsi a une certaine continuite entre les differentes etapes de la determination des proprietes physico-chimiques. Ce role d'interface est abondamment utilise au cours de ce travail. Ainsi, la parametrisation d'equations d'etat par la connaissance des parametres critiques des especes chimiques mises en jeu constitue l'essence de cet article. Dans le cadre d'une approche tout a fait generale, les methodes predictives et l'analyse statistique fournissent la clef pour estimer les parametres critiques. Nous avons opte pour la regression lineaire multiple impliquant des variables judicieusement choisies pour leur influence sur ces parametres critiques. Le choix des descripteurs repose sur la determination des proprietes influant sur la valeur de ces parametres critiques et est conditionne par la possibilite d'evaluer ces grandeurs a l'aide des methodes de chimie quantique.

Using a state-of-the-art time-dependent density functional (TD-DFT) approach that includes the explicit consideration of bulk medium effects on both the ground-state geometry and the electronic spectrum, we have determined the lambda(max) of 86 naphthoquinones (NQ) dyes in various solvents for a total of 151 cases. In most cases, TD-DFT provides the correct ordering of transitions for substituted NQ dyes. Comparisons with experimental values lead to a mean signed error of -7.2 nm (0.039 eV) and a mean absolute error of 20.1 nm (0.113 eV). It turns out that the average errors are smaller for the hydroxy and methoxy derivatives, than for amino substituted dyes. It is also demonstrated that the statistical treatment of the data does not significantly improve the agreement between the experimental and the theoretical values. We also discuss average basis set effects and solvatochromism.

The n --pi* transitions in more than 100 thiocarbonyl dyes have been calculated with an ab initio procedure relying on the combination of time-dependent density functional theory (TD-DFT) for evaluating excited states and the polarizable continuum model (PCM) for modeling the bulk solvent effects on both the geometrical and electronic structures. Two hybrid functionals (B3LYP and PBE0) and several basis sets, some including f polarization functions, have been used. B3LYP provides the most accurate raw estimates, but once simple linear regression is performed, both functionals give similar results with a small advantage for PBE0. By use of the latter, the mean absolute deviation with respect to experiment is limited to 0.06 eV whereas less than 20% of the estimates differ from absorption data by more than 0.10 eV. To assess the validity limits of our model, compounds containing multiple C=S chromophores have also been considered.

This chapter describes the derivation of size parameters for the SAFT-VRequation of state from quantum mechanical calculations. The chain length parameter, m , and the segment diameter, σ , for SAFT-VR are derived by mapping molecular dimensions calculated via the Restricted Hartree-Fock (HF) formalism onto a spherocylinder. The dimensions used are the molecular volume, calculated by integrating the electronic density, and the smallest and largest dimensions of a box containing the molecule. The molecular volume and the molecular aspect ratio as obtained from the HF calculation are then used to determine the SAFT parametes m and σ. Once m and σ have been computed, the remaining SAFT-VR parameters are estimated using experimental VLB data. The proposed approach is useful in several ways. Firstly, it allows a physical value for the chain length parameter m to be established. Secondly, the proposed approach leads to a reduction in the number of parameters which must be estimated by numerical optimisation, and therefore an increase in the statistical significance of those parameter values, especially when experimental data are scarce. Finally, by combining the proposed method with ab initio techniques to derive the other SAFT parameters, this work provides a stepping stone towards data-free methods to model the phase behaviour of new compounds.

This chapter discusses the estimation of critical parameters from quantum mechanics. The QSPR method combined with multiple linear regression is an efficient and elegant way to estimate from scratch the critical parameters of a wide range of compounds. Calculated critical parameters for pure compounds including extrapolation to the limit of extended systems are both in agreement with experimental data and values obtained by group contribution methods, though, in some cases, these contribution methods are unable to correctly describe the saturation behavior of critical temperature. To obtain the critical parameters for binary mixture, the Redlich's logarithmic-hyperbolic interpolation functions have been used. The great advantage of this method is that only critical parameters of pure compounds are required. Two mixtures have been studied butane-hexane, C0 2 -pentane. Calculated mixture critical values are in very good agreement with experimental data, illustrating that the combination of empirical rules and QM is possible and often valuable when carefully performed.

The UV/visible spectra of a series of indigo derivatives have been evaluated by using ab initio methods. The combination of the Polarizable continuum model for estimating bulk solvent effects with the TD-B3LYP∕6-311+G(2d,p)∕∕B3LYP∕6-311G(d,p) level of approximation, leads to an accurate description of the wavelength of maximum absorption of indigoids compounds. Using this procedure, we have assessed the effects of both the surroundings (solvent and solid state) and the substitution pattern. For the latter, we obtained a mean absolute deviation of only 7 nm (0.02 eV) compared to experiment, for a set of 86 molecules/solvents.

Bien souvent source d’anxiété, l’entrée à l’université n’est pas une étape anodine pour les étudiants. Ils savent en effet qu’ils vont devoir apprendre de manière plus indépendante et compter principalement sur leurs propres ressources plutôt que sur un appui continu de leurs enseignants. Le système d’évaluation diffère de celui proposé dans l’enseignement secondaire, durant lequel les étudiants ont pris l’habitude d’interagir avec leurs professeurs autour d’évaluations régulières et d’ainsi adapter en douceur leurs manières d’apprendre. Les difficultés autour de la transition entre l’enseignement secondaire et l’enseignement supérieur sont encore renforcées en Belgique par le système de libre accès et par l’absence d’examen externe standardisé en fin d’enseignement secondaire (du type baccalauréat en France). Ainsi, les étudiants ignorent si leur niveau de connaissances et de compétences est adéquat à une entrée confortable dans les études qu’ils ont librement choisies.