The Experts below are selected from a list of 7656 Experts worldwide ranked by ideXlab platform
Michele Parrinello  One of the best experts on this subject based on the ideXlab platform.

Ab Initio Simulation of water interaction with the 100 surface of pyrite
Journal of Chemical Physics, 2003CoAuthors: Andy C. Stirling, Marco Bernasconi, Michele ParrinelloAbstract:Car–Parrinello Simulations have been performed to study the interaction of water with pyrite (100) surface. The stAbility and the structural and electronic properties of both the molecular and dissociative adsorptions have been addressed. We found a very strong preference for molecular adsorption on the surface iron sites, in agreement with experiment. The dissociative chemisorption of water is energetically disfavored and is even locally unstAble; the dissociated fragments transform back to the stAble molecular form in a short molecular dynamics run. The calculations revealed that hydrogen bonding plays an important role in the stAbilization of the adsorbed water for both the molecular and the dissociative states. We have shown that water forms a coordinative covalent bond with the surface iron atoms by donating electron to the empty iron dz2 orbitals which are the lowest empty states on the clean surface. At full coverage, the sulfur 3p states thus become the lowest availAble empty states and therefore the subject of possible electrontransfer reactions.Car–Parrinello Simulations have been performed to study the interaction of water with pyrite (100) surface. The stAbility and the structural and electronic properties of both the molecular and dissociative adsorptions have been addressed. We found a very strong preference for molecular adsorption on the surface iron sites, in agreement with experiment. The dissociative chemisorption of water is energetically disfavored and is even locally unstAble; the dissociated fragments transform back to the stAble molecular form in a short molecular dynamics run. The calculations revealed that hydrogen bonding plays an important role in the stAbilization of the adsorbed water for both the molecular and the dissociative states. We have shown that water forms a coordinative covalent bond with the surface iron atoms by donating electron to the empty iron dz2 orbitals which are the lowest empty states on the clean surface. At full coverage, the sulfur 3p states thus become the lowest availAble empty states and therefore ...

Ab Initio Simulation of water interaction with the (100) surface of pyrite
Journal of Chemical Physics, 2003CoAuthors: Andy C. Stirling, Marco Bernasconi, Michele ParrinelloAbstract:A microscopic description of water interaction with the (100) surface of pyrite was estAblished by means of Ab Initio molecular dynamics Simulations. It was found that water preferentially adsorbs molecularly on iron sites at low and high coverages.

Surface solvation of halogen anions in water clusters: An Ab Initio molecular dynamics study of the Cl(H2O)(6) complex
J. Chem. Phys., 2001CoAuthors: Douglas J Tobias, Pavel Jungwirth, Michele ParrinelloAbstract:The structure and dynamics of Cl(H2O)(6) has been studied by Ab Initio molecular dynamics using the CarParrinello approach, and compared to results of Ab Initio quantum chemical calculations, molecular dynamics based on both polarizAble and nonpolarizAble empirical potentials, and vibrational spectroscopy. The electronic structure methodology (density functional theory with the gradientcorrected BLYP exchangecorrelation functional) used in the CarParrinello dynamics has been shown to give good agreement with secondorder MollerPlesset results for the structures and energies of Cl(H2O)(n), n=14, clusters. The configurational sampling during the 5 ps Ab Initio molecular dynamics Simulation at 250 K was sufficient to demonstrate that the chloride anion preferred a location on the surface of the cluster which was significantly extended compared to the minimum energy geometry. The structure of the cluster predicted by the polarizAble force field Simulation is in agreement with the Ab Initio Simulation, while the nonpolarizAble force field calculation was in qualitative disagreement, predicting an interior location for the anion. The time evolution of the electronic structure during the Ab Initio Simulation was analyzed in terms of maximally localized orbitals (Wannier functions). Calculation of the dipole moments from the centers of the Wannier orbitals revealed that the chloride anion is significantly polarized, and that the extent of water polarization depends on location in the cluster, thus underscoring the importance of electronic polarization in halogen ion solvation. The infrared Absorption spectrum was computed from the dipoledipole correlation function, including both nuclear and electronic contributions. Aside from a systematic redshift by 3%5% in the frequencies, the computed spectrum was in quantitative agreement with vibrational predissociation data on Cl(H2O)(5). Our analysis suggests that accounting for anharmonicity and couplings between modes is more important than the fine tuning of the electronic structure method for the quantitative prediction of hydrogen bond dynamics in aqueous clusters at elevated temperatures. (C) 2001 American Institute of Physics.

Ab Initio Simulation OF ROTATIONAL DYNAMICS OF SOLVATED AMMONIUM ION IN WATER
Journal of the American Chemical Society, 1999CoAuthors: Filippo Brugé, Marco Bernasconi, Michele ParrinelloAbstract:We have performed an Ab Initio molecular dynamics Simulation of the rotational dynamics of NH4+ ion in water. This work was motivated by the experimental evidence that the solvated NH4+ rotates rather fast, despite the expected formation of strong hydrogen bonds with water. We find that NH4+ is on average coordinated with five water molecules. Four water molecules form a longlived tetrahedral cage around the ion, each molecule being hydrogenbonded with one proton of NH4+. The fifth water molecule is much more mobile and occasionally exchanges with one of the four molecules in the tetrahedral cage. The hydrogen bonding of NH4+ with water is strong enough to prevent the free rotation of the ion, which instead tumbles in a sequence of discontinuous rotational jumps associated with the exchange of two water molecules in the tetrahedral cage. The simulated rotational dynamics is consistent with nuclear magnetic resonance data and encourages the use of Ab Initio Simulations to describe the solvation of ions i...

AbInitio Simulation of Solid State Polymerization of Acetylene Under Pressure
MRS Proceedings, 1997CoAuthors: Marco Bernasconi, Michele Parrinello, G. L. Chiarotti, P. Focher, Erio TosattiAbstract:AbSTRACTWe have recently devised a new method for the Ab Initio Simulation of solidsolid phase transformations under pressure. The method is here applied to the study of the solidstate polymerization of acetylene under pressure and the generation of hydrogenated amorphous carbon from compression of polyacetylene.
Andy C. Stirling  One of the best experts on this subject based on the ideXlab platform.

Ab Initio Simulation of water interaction with the 100 surface of pyrite
Journal of Chemical Physics, 2003CoAuthors: Andy C. Stirling, Marco Bernasconi, Michele ParrinelloAbstract:Car–Parrinello Simulations have been performed to study the interaction of water with pyrite (100) surface. The stAbility and the structural and electronic properties of both the molecular and dissociative adsorptions have been addressed. We found a very strong preference for molecular adsorption on the surface iron sites, in agreement with experiment. The dissociative chemisorption of water is energetically disfavored and is even locally unstAble; the dissociated fragments transform back to the stAble molecular form in a short molecular dynamics run. The calculations revealed that hydrogen bonding plays an important role in the stAbilization of the adsorbed water for both the molecular and the dissociative states. We have shown that water forms a coordinative covalent bond with the surface iron atoms by donating electron to the empty iron dz2 orbitals which are the lowest empty states on the clean surface. At full coverage, the sulfur 3p states thus become the lowest availAble empty states and therefore the subject of possible electrontransfer reactions.Car–Parrinello Simulations have been performed to study the interaction of water with pyrite (100) surface. The stAbility and the structural and electronic properties of both the molecular and dissociative adsorptions have been addressed. We found a very strong preference for molecular adsorption on the surface iron sites, in agreement with experiment. The dissociative chemisorption of water is energetically disfavored and is even locally unstAble; the dissociated fragments transform back to the stAble molecular form in a short molecular dynamics run. The calculations revealed that hydrogen bonding plays an important role in the stAbilization of the adsorbed water for both the molecular and the dissociative states. We have shown that water forms a coordinative covalent bond with the surface iron atoms by donating electron to the empty iron dz2 orbitals which are the lowest empty states on the clean surface. At full coverage, the sulfur 3p states thus become the lowest availAble empty states and therefore ...

Ab Initio Simulation of water interaction with the (100) surface of pyrite
Journal of Chemical Physics, 2003CoAuthors: Andy C. Stirling, Marco Bernasconi, Michele ParrinelloAbstract:A microscopic description of water interaction with the (100) surface of pyrite was estAblished by means of Ab Initio molecular dynamics Simulations. It was found that water preferentially adsorbs molecularly on iron sites at low and high coverages.
Marco Bernasconi  One of the best experts on this subject based on the ideXlab platform.

Ab Initio Simulation of water interaction with the 100 surface of pyrite
Journal of Chemical Physics, 2003CoAuthors: Andy C. Stirling, Marco Bernasconi, Michele ParrinelloAbstract:Car–Parrinello Simulations have been performed to study the interaction of water with pyrite (100) surface. The stAbility and the structural and electronic properties of both the molecular and dissociative adsorptions have been addressed. We found a very strong preference for molecular adsorption on the surface iron sites, in agreement with experiment. The dissociative chemisorption of water is energetically disfavored and is even locally unstAble; the dissociated fragments transform back to the stAble molecular form in a short molecular dynamics run. The calculations revealed that hydrogen bonding plays an important role in the stAbilization of the adsorbed water for both the molecular and the dissociative states. We have shown that water forms a coordinative covalent bond with the surface iron atoms by donating electron to the empty iron dz2 orbitals which are the lowest empty states on the clean surface. At full coverage, the sulfur 3p states thus become the lowest availAble empty states and therefore the subject of possible electrontransfer reactions.Car–Parrinello Simulations have been performed to study the interaction of water with pyrite (100) surface. The stAbility and the structural and electronic properties of both the molecular and dissociative adsorptions have been addressed. We found a very strong preference for molecular adsorption on the surface iron sites, in agreement with experiment. The dissociative chemisorption of water is energetically disfavored and is even locally unstAble; the dissociated fragments transform back to the stAble molecular form in a short molecular dynamics run. The calculations revealed that hydrogen bonding plays an important role in the stAbilization of the adsorbed water for both the molecular and the dissociative states. We have shown that water forms a coordinative covalent bond with the surface iron atoms by donating electron to the empty iron dz2 orbitals which are the lowest empty states on the clean surface. At full coverage, the sulfur 3p states thus become the lowest availAble empty states and therefore ...

Ab Initio Simulation of water interaction with the (100) surface of pyrite
Journal of Chemical Physics, 2003CoAuthors: Andy C. Stirling, Marco Bernasconi, Michele ParrinelloAbstract:A microscopic description of water interaction with the (100) surface of pyrite was estAblished by means of Ab Initio molecular dynamics Simulations. It was found that water preferentially adsorbs molecularly on iron sites at low and high coverages.

Ab Initio Simulation OF ROTATIONAL DYNAMICS OF SOLVATED AMMONIUM ION IN WATER
Journal of the American Chemical Society, 1999CoAuthors: Filippo Brugé, Marco Bernasconi, Michele ParrinelloAbstract:We have performed an Ab Initio molecular dynamics Simulation of the rotational dynamics of NH4+ ion in water. This work was motivated by the experimental evidence that the solvated NH4+ rotates rather fast, despite the expected formation of strong hydrogen bonds with water. We find that NH4+ is on average coordinated with five water molecules. Four water molecules form a longlived tetrahedral cage around the ion, each molecule being hydrogenbonded with one proton of NH4+. The fifth water molecule is much more mobile and occasionally exchanges with one of the four molecules in the tetrahedral cage. The hydrogen bonding of NH4+ with water is strong enough to prevent the free rotation of the ion, which instead tumbles in a sequence of discontinuous rotational jumps associated with the exchange of two water molecules in the tetrahedral cage. The simulated rotational dynamics is consistent with nuclear magnetic resonance data and encourages the use of Ab Initio Simulations to describe the solvation of ions i...

AbInitio Simulation of Solid State Polymerization of Acetylene Under Pressure
MRS Proceedings, 1997CoAuthors: Marco Bernasconi, Michele Parrinello, G. L. Chiarotti, P. Focher, Erio TosattiAbstract:AbSTRACTWe have recently devised a new method for the Ab Initio Simulation of solidsolid phase transformations under pressure. The method is here applied to the study of the solidstate polymerization of acetylene under pressure and the generation of hydrogenated amorphous carbon from compression of polyacetylene.

AbInitio Simulation of phase transformations under pressure
Physica Scripta, 1996CoAuthors: Marco Bernasconi, Michele Parrinello, M Benoit, G. L. Chiarotti, P. Focher, Erio TosattiAbstract:We have recently devised a new method for Ab Initio Simulation of solidsolid phase transformation under pressure. The method is here applied to the study of ice at Mbar pressure, the solidstate polymerization of acetylene under pressure and the generation of taC: H from compression of polyacetylene.
Yang Leng  One of the best experts on this subject based on the ideXlab platform.

Ab Initio Simulation on the crystal structure and elastic properties of carbonated apatite
Journal of The Mechanical Behavior of Biomedical Materials, 2013CoAuthors: Xiong Lu, Yang LengAbstract:Ab Initio quantum mechanical (QM) calculations were employed to study the crystal structure and elastic properties of carbonated apatite (CAp). Two locations for the carbonate ion in the apatite lattice were considered: carbonate substituting for OH− ion (typeA), and for PO43− ion (typeB) with possible charge compensation mechanisms. A combined typeAb substitution (two carbonate ions replacing one phosphate group and one hydroxyl group, respectively) was also investigated. The results show that the most energetically stAble substitution is typeAb, followed by typeA and then typeB. The most stAble configuration of typeA has its carbonate triangular plane almost parallel to caxis at z=0.46. The lowest energy configuration of typeB is that with a sodium ion substituting for a calcium ion for charge balance and the carbonate lying on the b/cplane of apatite. Lattice parameter changes after carbonate substitution in hydroxyapatite (HA) agree with reported experimental results qualitatively: for typeA, lattice parameter a increases but c decreases; and for typeB, lattice parameter a decreases but c increases. Using the calculated CAp stAble structures, we also calculated the elastic properties of CAp and compared them with those of HA and biological apatites.

synthesis characterization and Ab Initio Simulation of magnesium substituted hydroxyapatite
Acta Biomaterialia, 2010CoAuthors: Yang Leng, Xiang GeAbstract:Abstract The substitution of magnesium in hydroxyapatite (HA) was examined in HA nanocrystals synthesized by the wetchemical precipitation method at 90 °C. Comprehensive characterization techniques, including Xray diffraction, Xray fluorescence, field emission scanning electron microscopy, highresolution transmission electron microscopy, thermogravimetric analysis and Rietveld refinement, provided experimental evidence of the effects of Mg substitution on the phase, crystallinity, chemical composition, crystal size, morphology, thermal stAbility and crystal lattice structure of HA. A computational study using Ab Initio generalized gradient approximation density functional theory was performed to reveal changes in lattice parameters and preferential calcium sites for Mg substitution in HA. The experimental results showed that a limited amount of Mg (Mg/(Mg + Ca) between 5 and 7 mol.%) could successfully substitute for Ca in HA. HA crystallites became smaller and more irregular, and they formed greater agglomerates with Mg substitution. Mg substitution resulted in decreases in the crystallinity and thermal stAbility of HA. The lattice constants, a and c, decreased with increasing Mg substitution. The Simulation results revealed that the Ca(1) sites in HA lattices were energetically favored sites for Mg substitution.
Alain Pasturel  One of the best experts on this subject based on the ideXlab platform.

Investigation of molybdenum and caesium behaviour in urania by Ab Initio calculations.
2009CoAuthors: G. Brillant, F. Gupta, Alain PasturelAbstract:A theoretical study of molybdenum and caesium solution in uranium dioxide is carried out. Calculations are performed using the density functional theory with the projectoraugmentedwave method as implemented in the Vienna Ab Initio Simulation package (VASP). Correlation effects are taken into account within the DFT+U approach. Molybdenum is preferentially inserted in uraniumoxygen divacancies for understoichiometric urania and uranium vacancies for overstoichiometric urania. The favourAble sites for caesium solution are the Schottky defect for understoichiometric urania and U vacancies and UO divacancies for overstoichiometric urania. Using the stAbility of many binary and ternary compounds in comparison to soluted atoms, we show that caesium and molybdenum are insoluble in uranium dioxide whatever the stoichiometric regime.

Ab Initio study of solution energy and diffusion of caesium in uranium dioxide
2009CoAuthors: F. Gupta, Alain Pasturel, G. BrillantAbstract:The behaviour of caesium in nuclear fuels is investigated using density functional theory (DFT). In a first step, the incorporation and solution energies of Cs in preexisting trap sites of UO2 (vacancies, interstitials, UO divacancy and Schottky trio defects) are calculated using the projectoraugmentedwave (PAW) derived pseudopotentials as implemented in the Vienna Ab Initio Simulation package (VASP). Correlation effects are taken into account within the DFT + U approach. The solubility of caesium is found to be very low, in agreement with experimental data. The migration of Cs is found to be highly anisotropic, it is controlled by uranium diffusion with an Arrhenius activation energy of 4.8 eV in hyperstoichiometric UO2+x, in good agreement with experimental values. © 2008 Elsevier B.V. All rights reserved.

Correlation effects and energetics of point defects in uranium dioxide: a first principle investigation
2007CoAuthors: F. Gupta, G. Brillant, Alain PasturelAbstract:Density functional (DFT) calculations have been used to investigate the stAbility of point defects in uranium dioxide. Correlation effects are taken into account within the DFT+U approach as implemented in the Vienna Ab Initio Simulation package (VASP). More particularly, the formation energies of both intrinsic and extrinsic point defects, i.e. vacancies, interstitials, Frenkel pairs and Schottky trio defects, are calculated. Our results are compared with availAble experimental data and are also discussed in relation to previous calculations based on conventional functionals, such as the local spindensity approximation and generalized gradient approximations.