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Ab Initio Simulation

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Michele Parrinello – 1st expert on this subject based on the ideXlab platform

  • Ab Initio Simulation of water interaction with the 100 surface of pyrite
    Journal of Chemical Physics, 2003
    Co-Authors: Andy C. Stirling, Marco Bernasconi, Michele Parrinello

    Abstract:

    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 electron-transfer 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, 2003
    Co-Authors: Andy C. Stirling, Marco Bernasconi, Michele Parrinello

    Abstract:

    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., 2001
    Co-Authors: Douglas J Tobias, Pavel Jungwirth, Michele Parrinello

    Abstract:

    The structure and dynamics of Cl-(H2O)(6) has been studied by Ab Initio molecular dynamics using the Car-Parrinello 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 gradient-corrected BLYP exchange-correlation functional) used in the Car-Parrinello dynamics has been shown to give good agreement with second-order Moller-Plesset results for the structures and energies of Cl-(H2O)(n), n=1-4, 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 dipole-dipole 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.

Andy C. Stirling – 2nd expert on this subject based on the ideXlab platform

  • Ab Initio Simulation of water interaction with the 100 surface of pyrite
    Journal of Chemical Physics, 2003
    Co-Authors: Andy C. Stirling, Marco Bernasconi, Michele Parrinello

    Abstract:

    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 electron-transfer 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, 2003
    Co-Authors: Andy C. Stirling, Marco Bernasconi, Michele Parrinello

    Abstract:

    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 – 3rd expert on this subject based on the ideXlab platform

  • Ab Initio Simulation of water interaction with the 100 surface of pyrite
    Journal of Chemical Physics, 2003
    Co-Authors: Andy C. Stirling, Marco Bernasconi, Michele Parrinello

    Abstract:

    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 electron-transfer 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, 2003
    Co-Authors: Andy C. Stirling, Marco Bernasconi, Michele Parrinello

    Abstract:

    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, 1999
    Co-Authors: Filippo Brugé, Marco Bernasconi, Michele Parrinello

    Abstract:

    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 long-lived tetrahedral cage around the ion, each molecule being hydrogen-bonded 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…