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  • 1.
    Agosta, Lorenzo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Atomistic simulations of structural and dynamical properties of liquids under geometric constraints2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The statistical-mechanical description of liquids represents a formidable problem in physic due to the absence of the analytical theory of the liquid state. Atomistic simulations represent a unique source of information in this respect and can be implemented in order address macroscopically measurable liquid properties, including its structure and dynamics, based on the information of the interactions between its constituent molecules. A particularly intriguing challenge is represented by the problem of studying liquids under geometric constraints like surfaces, or where the dimensionality is strongly suppressed like for liquids in 2 dimensions. Experimental measurements cannot access to these regions due to the resolution limitations. In this thesis the study of confined liquids is achieved by particle-based simulations at different level of theory. In particular 3 study cases are considered: the first is the characterization of solid-liquid interfaces. The problem of adsorbing surfaces is treated as a specific case of inorganic surfaces in contact with liquid water. TiO2, chosen as reference material, is studied in its polymorphic structures in aqueous conditions. The surface reactivity and its influence on the liquid structure is solved considering the quantum nature of the system. The mechanism of a solute adsorbing at the interface, considering the interfacial liquid properties, is also addressed. New advanced analysis tools for determining the structural and dynamical properties of water under a surface confinement and the thermodynamic associated to relative adsorption processes are developed. We are confident that this study will represent a mile stone for a systematic study of complex environments as bio-inorganic interfaces. As second case a liquid confined in a 2D surface is studied. Simple liquids having spherically symmetric interaction are very powerful in order to understand the relevant degrees of freedom that governs a certain physical process. Here we expand the definition of 2D hexatic phases to smectic systems in 3D. Finally the self-assembly of a triply periodic mesophase having a Fddd space symmetry group is fully characterized for a simple liquid. This phase can be thought as a geometrical reduction to a two-dimensional separation surface. The possibility of generating such complex network with simple particles, like in colloids, opens the frontiers for the exploration of new materials and applications.

  • 2.
    Agosta, Lorenzo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Thermodynamic and electronic characterization of Glycine adsorbing on TiO2 anatase (101) surface from first principles simulationsManuscript (preprint) (Other academic)
  • 3.
    Agosta, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brandt, Erik G.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 2, article id 024704Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics simulations are reported forwater-embedded TiO2 surfaces to determine the diffusive and reactive behavior at full hydration. A three-domain model is developed for six surfaces [rutile (110), (100), and (001), and anatase (101), (100), and (001)] which describes waters as hard (irreversibly bound to the surface), soft (with reduced mobility but orientation freedom near the surface), or bulk. The model explains previous experimental data and provides a detailed picture of water diffusion near TiO2 surfaces. Water reactivity is analyzed with a graph-theoretic approach that reveals a number of reaction pathways on TiO2 which occur at full hydration, in addition to direct water splitting. Hydronium (H3O+) is identified to be a key intermediate state, which facilitates water dissociation by proton hopping between intact and dissociated waters near the surfaces. These discoveries significantly improve the understanding of nanoscale water dynamics and reactivity at TiO2 interfaces under ambient conditions.

  • 4.
    Agosta, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brandt, Erik G.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Improved Sampling in Ab Initio-Based Free Energy Calculations of Amino Acids at Solid-Liquid Interfaces: A Tight-Binding Assessment on TiO2 Anatase (101)Manuscript (preprint) (Other academic)
    Abstract [en]

    Atomistic simulations are powerful for probing molecules at bioinorganic interfaces and excellent complements to scarcely available experimental techniques. The free energy controls the adsorption behavior of molecules on nanosurfaces, and is therefore a quantity of particular importance. Advanced sampling techniques can efficiently explore the adsorption free energy landscape, but molecular simulations with classical (Newtownian) dynamics fail to capture charge transfer and polarization at the solid-liquid interface. First principle simulations do not suffer from this limitation but come with a heavy computational load. Here, we introduce an efficient protocol to explore the free energy of adsorption in the ab initio framework. This approach accurately models the complex phenomena at bio-inorganic surfaces on the nanoscale and properly samples the relevant thermodynamic properties. We present a case study of adsorption of the Lysine and Aspartate amino acids on the anatase (101) TiO2 surface with the tight binding method. The high values of the calculated adsorption free energies highlight the importance of a proper description of the electronic state for surface binding processes.

  • 5.
    Agosta, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Metere, Alfredo
    Dzugutov, Mikhail
    Hexatic smectic phase with algebraically decaying bond-orientational order2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 5, article id 052702Article in journal (Refereed)
    Abstract [en]

    The hexatic phase predicted by the theories of two-dimensional melting is characterized by the power-law decay of the orientational correlations, whereas the in-layer bond orientational order in all the hexatic smectic phases observed so far was found to be long range. We report a hexatic smectic phase where the in-layer bond orientational correlations decay algebraically, in quantitative agreement with the hexatic ordering predicted by the theory for two dimensions. The phase was formed in a molecular dynamics simulation of a one-component system of particles interacting via a spherically symmetric potential. The present results thus demonstrate that the theoretically predicted two-dimensional hexatic order can exist in a three-dimensional system.

  • 6.
    Agosta, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Metere, Alfredo
    Oleynikov, Peter
    Dzugutov, Mikhail
    Self-assembly of orthorhombic Fddd network in simple one-component liquidsManuscript (preprint) (Other academic)
    Abstract [en]

    Triply periodic continuous morphologies arising a result of the microphase separation in block copolymer melts have so far never been observed self-assembled in systems of particles with spherically symmetric interaction. We report a molecular dynamics simulation of two simple one-component liquids which self-assemble upon cooling into equilibrium orthorhombic continuous network morphologies with the Fddd space group symmetry reproducing the structure of those observed in block copolymers. The finding that the geometry of constituent molecules isn't relevant for the formation of triply periodic networks indicates the generic nature of this class of phase transition.

  • 7.
    Brandt, Erik G.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Agosta, Lorenzo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Reactive wetting properties of TiO2 nanoparticles predicted by ab initio molecular dynamics simulations2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 27, p. 13385-13398Article in journal (Refereed)
    Abstract [en]

    Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity.

  • 8. Gala, Fabrizio
    et al.
    Agosta, Lorenzo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zollo, Giuseppe
    Water Kinetics and Clustering on the (101) TiO2 Anatase Surface2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 1, p. 450-456Article in journal (Refereed)
    Abstract [en]

    (101) anatase TiO2 surface in water ambient is an important system for the interaction of biocompatible nanodevices with biological environment. Following the experimental evidence showing that water molecules are mobile at temperature as low as 190 K and tend to form clusters along the [11 (1) over bar]/[1 (11) over bar] surface directions, a complete theoretical characterization of the dynamical properties of the first water layer on the (101) anatase TiO2 surface is presented. A variety of computational techniques have been employed in the context of the transition-state theory in the harmonic regime, ranging from first-principles total energy ground-state calculations, to density functional perturbation theory, minimum energy path search, and kinetic Monte Carlo simulations, to explain the experimental results on water kinetics on the (101) anatase TiO2 surface. We have calculated the migration energy barrier of water molecules, the vibrational prefactor through the phonon density of states, and the hopping rate along two principal directions. Lastly, in a kinetic Monte Carlo context, we have simulated and clarified the dynamical processes that are on the basis of the observed experimental behavior.

  • 9. Vitale, Eugenio
    et al.
    Zollo, Giuseppe
    Agosta, Lorenzo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gala, Fabrizio
    Brandt, Erik G.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stress Relief and Reactivity Loss of Hydrated Anatase (001) Surface2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 39, p. 22407-22417Article in journal (Refereed)
    Abstract [en]

    Dissociative and molecular water adsorption on the anatase (001) surface is studied in the context of state-of-the-art density functional theory in large supercells suited for adsorption studies at various water coverage ratios. At low coverage values below 1/4 ML, water adsorption remains dissociative and a network of hydrogen bonds between the so formed hydroxyl groups favors the formation of a ridge surface structure. The hydroxyl patterned (4 X 4) surface thus undergoes a (2 X 4) reconstruction that causes the relief of the large tensile stress measured in the unreconstructed surface along the direction orthogonal to the ridge. This phenomenology is accompanied by the loss of reactivity of the reconstructed surface with respect to the dissociative water adsorption that becomes molecular above 1/4 ML. We also show that the molecular adsorption on the terrace is weaker than the one on the ridge. The present water reconstruction model is discussed and compared to the well-known ADM model of the reconstructed anatase (001) surface in dry environment.

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