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Accurate description of thermodynamic, structural, and electronic properties for bulk and surfaces of ceria (CeO2) necessitates the inclusion of the Hubbard parameter (U) in the density functional theory (DFT) calculations to precisely account for the strongly correlated 4f electrons. Such treatment is a daunting task when attempting to draw a potential energy surface for CeO2-catalyzed reaction. This is due to the inconsistent change in thermo-kinetics parameters of the reaction in reference to the variation in the U values. As an illustrative example, we investigate herein the discrepancy in activation and reaction energies for steps underlying the partial and full hydrogenation of acetylene over the Ce[O.sub.2](111) surface. Overall, we find that both activation and reaction energies positively correlate with the increase in the U value. In addition to benchmarking against more accurate theoretical methodologies, we suggest that U values are better optimized against kinetics modelling of experimentally observed profiles of products from the catalytic-assisted system of reactions. Key words: ceria, DFT + U, reaction barriers, hydrogenation of acetylene, catalysts, transition state, Hubbard parameter (U). Une description precise des proprietes thermodynamiques, structurelles et electroniques de volume et de surface de l'oxyde de cerium (CeO2) requiert l'inclusion du parametre de Hubbard (U) dans le cadre d'un calcul en theorie de la fonctionnelle de densite (TFD), afin de tenir compte de facon precise des electrons 4f fortement correles. Un tel calcul est un defi important lorsqu'on tente d'obtenir la surface d'energie potentielle pour une reaction catalysee par Ce[O.sub.2]. Ceci est du au changement incoherent dans les parametres de reaction face a la variation de la valeur de U. Comme exemple illustratif, nous examinons ici le desaccord entre les energies d'activation et de reaction dans les etapes sous-jacentes a l'hydrogenation partielle et complete de l'acetylene sur une surface (111) de Ce[O.sub.2]. En resume, nous trouvons que ces deux energies sont correlees positivement avec l'augmentation de U. De plus, comme reference face a des methodes theoriques plus precises, nous suggerons d'optimiser les valeurs de U selon la modelisation cinetique des profils experimentaux de produits de reactions assistees par catalyse. [Traduit par la Redaction] Mots-cles : oxyde de cerium, hydrogenation, barriere de reaction, TFD, catalyse., 1. Introduction Cerium oxide (CeO2, ceria) and materials based on it are essential in many strategic catalytic industrial applications [1-3]. As oxygen-storage ingredients [4], they are utilized in three-way catalysts [...]

This contribution aims to investigate volume-dependent thermal and mechanical properties of the two most studied phases of molybdenum nitride (c-MoN and h-MoN) by means of the quasi-harmonic approximation approach (QHA) via first-principles calculations up to their melting point and a pressure of 12 GPa. Lattice constants, band gaps, and bulk modulus at 0 K match corresponding experimental measurements well. Calculated Bader's charges indicate that Mo-N bonds exhibit a more ionic nature in the cubic MoN phase. Based on estimated Gibbs free energies, the cubic phase presents thermodynamic stability higher than that detected for hexagonl, with no phase transition observed in the selected T-P conditions as detected experimentally. The elastic stiffness coefficients of MoN in hexagonal structure revealed that it is stable elastically; in contrast to the cubic structure. The temperature dependence on the bulk modulus is more profound on the dense cubic phase than on the hexagonal phase. Overall, the two considered structures of molybdenum nitride display very minimal harmonic effects, evidenced by the slight variation of thermal and mechanical properties with the increase of pressure and temperature. The optical conductivity of both phases near a zero photon energy coincides well with their metallic character inferred by their corresponding DOS curves. It is expected that the thermo-elastic properties of saturated molybdenum nitrides reported in this study will aid in the continuous pursuit to enhance their catalytic and mechanical utilizations. Key words: density functional theory, thermo-elastic properties, molybdenum nitride. Nous entreprenons ici une etude des proprietes thermiques et mecaniques dependantes en volume des deux phases les plus etudiees du nitrure de molybdene (c-MoN et h-MoN), a l'aide de l'approximation quasi-harmonique (AQH/QHA) via des calculs a partir de principes premiers, jusqu'au point de fusion et a des pressions de 12 GPa. Les valeurs calculees des constantes de reseau, des bandes interdites et du module d'elasticite volumique a 0 K correspondent bien aux mesures experimentales. Le calcul des charges de Bader indique que le lien Mo-N est plus ionique dans la phase cubique c-MoN. Sur la base des energies libres de Gibbs estimees, la phase cubique presente une meilleure stabilite thermodynamique que la phase hexagonale, sans transition de phase observee dans les conditions T-P fixees, tel qu'observe experimentalement. Les coefficients de rigidite de MoN dans la phase hexagonale montrent que cette structure est elastiquement stable, contrairement a la phase cubique. La dependance en temperature du module d'elasticite volumique est plus importante dans la phase cubique que dans la phase hexagonale. Dans l'ensemble, les deux structures etudiees ici de nitrure de molybdene montrent tres peu d'effets harmoniques, ce qui est rendu evident par la faible variation des proprietes thermiques et mecaniques avec les augmentations de pression et de temperature. La conductivite optique des deux phases pour des photons de tres faible energie coincide bien avec leur caractere metallique suggere par leurs courbes DOS correspondantes. Nous croyons que les proprietes thermo-elastiques du nitrure de molybdene presentees ici aideront la poursuite de leurs utilisations catalytiques et mecaniques. [Traduit par la Redaction] Mots-cles: theorie de la fonctionnelle de densite, proprietes thermo-elastiques, nitrure de molybdene., 1. Introduction Owing to an array of remarkable properties, molybdenum has been at the centre of a great deal of research as it constitutes the parent metal of various carbides, [...]

Adding impurities or doping through adsorption is an effective way to tailor the properties of graphene-based materials. The capability of making predictions with regard to the trends of elemental adsorption on graphene is crucial to a better understanding of the more complex adsorption cases. It also provides useful guidelines for fabricating 2D graphene materials with novel properties. In this review, we show trends of elemental adsorption on graphene with elements of the periodic table, based on previous studies and supplemented with our recent calculations. We also discuss the effects of atomic ratios on some properties of this element-adsorbed graphene system. Trends of properties studied include binding energy, most stable site, adatom height, migration energy, Fermi energy shift, graphene distortion, magnetization, charge transfer, and electronic energy band gap at Fermi energy. Certainly, there is ample scope to investigate the electronic structures of elemental adsorption on graphene based on period and group of the periodic table, and atomic ratio. Key words: graphene, DFT, adatom, adsorption, band gap. L'ajout d'impuretes ou le dopage via l'adsorption est une facon efficace pour ajuster les proprietes des materiaux bases sur le graphene. Notre capacite a faire des predictions regardant les tendances de l'adsorption d'elements sur du graphene est tres importante dans le but de mieux comprendre les cas d'adsorption plus complexes. Elle s'avere egalement utile comme guide pour fabriquer des materiaux 2D a base de graphene et ayant des proprietes nouvelles. Dans cette revue, nous montrons les tendances d'adsorption des elements du tableau periodique, en se basant sur des etudes anterieures supplementees de nos calculs recents. Nous analysons aussi les effets des rapports atomiques sur certaines proprietes de ce systeme de graphene a adsorption d'elements. Les proprietes etudiees incluent l'energie de liaison, le site le plus stable, la hauteur d'adatomes, l'energie de migration, le deplacement de l'energie de Fermi, la distorsion du graphene, la magnetisation, le transfert de charge et la bande electronique interdite a l'energie de Fermi. De toute evidence, il y a amplement de choses a etudier sur la structure electronique suivant l'adsorption d'elements sur du graphene, selon la periode et le groupe du tableau periodique et le rapport atomique. [Traduit par la Redaction] Mots-cles: graphene, DFT, adatome ou atome adsorbe, adsorption, bande interdite. PACS Nos.: 73.20.At, 73.20.Hb, 73.22.Pr., 1. Introduction Graphene is a two-dimensional hexagonal lattice made of carbon atoms with nearest distance between the carbon atoms = 1.42 Å (1Å = [10.sup.-10] m). It became a 'marvel' [...]

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