| 1. |
- Agosta, Lorenzo, et al.
(författare)
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Hexatic smectic phase with algebraically decaying bond-orientational order
- 2018
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Ingår i: Physical review. E. - : American Physical Society. - 2470-0045 .- 2470-0053. ; 97:5
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Agosta, Lorenzo, et al.
(författare)
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Origin of the Hydrophobic Behaviour of Hydrophilic CeO2
- 2023
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Ingår i: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 62:35
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the hydrophobicity found in rare-earth oxides is intriguing. The CeO2 (100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter-intuitive effect we performed a detailed analysis of the water structure and dynamics. We report here an ab-initio molecular dynamics simulation (AIMD) study which demonstrates that the first water layer, in immediate contact with the hydroxylated CeO2 surface, is responsible for the effect behaving as a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways: a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H-bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare-earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.
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| 3. |
- Agosta, Lorenzo, et al.
(författare)
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Self-assembly of a triply periodic continuous mesophase with Fddd symmetry in simple one-component liquids
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:19
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Tidskriftsartikel (refereegranskat)abstract
- Triply periodic continuous morphologies (networks) arising as 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 where two simple one-component liquids form upon cooling an equilibrium network with the Fddd space group symmetry. This complexity reduction in the liquid network formation in terms of the particle geometry and the number of components evidences the generic nature of this class of phase transition, suggesting opportunities for producing these structures in a variety of new systems.
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| 4. |
- Agosta, Lorenzo, et al.
(författare)
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Self-assembly of orthorhombic Fddd network in simple one-component liquids
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Agosta, Lorenzo, et al.
(författare)
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Supercooled liquid-like dynamics in water near a fully hydrated titania surface : Decoupling of rotational and translational diffusion
- 2021
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:9
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Tidskriftsartikel (refereegranskat)abstract
- We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO2 on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation-translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation-translation decoupling in an ab initio MD simulation of water.
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| 6. |
- Davis, Sergio, 1978-
(författare)
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Atomistic Computer Simulations of the Melting Process and High Pressure Conditions
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work describes the use of atomistic computer simulations in the area of Condensed Matter Physics, and specifically its application to the study of two problems: the dynamics of the melting phase transition and the properties of materials at extreme high pressures and temperatures, problems which defy experimental measurements and purely analytical calculations. Both classical Molecular Dynamics (using semi–empirical interaction potentials) and first–principles (ab initio) Molecular Dynamics techniques has been applied in this study to the calculation of melting curves in a wide range of pressures for elements such as Xe and H2, the study of the elastic constants of Fe at the conditions of the Earth’s inner core, and the characterization of diffusion and defects formation in a generic Lennard–Jones crystal at the limit of superheating, including the role they play in the triggering of the melting process itself.
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| 7. |
- Elenius, Måns, 1974-, et al.
(författare)
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A polyamorphous fragile to strong transition under equilibrium cooling in a simple monatomic liquid
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Glass transition remains one of the deepest and most interesting problems of condensed-matter physics. One fundamental aspect of the problem is how to avoid crystalline nucleation when cooling a liquid towards the glass transition at an arbitrarily slow rate. The prototype ``ideal glass formers'' are silica and other inorganic network-forming systems. No monatomic glass has been obtained so far by cooling from melt. Whether a monatomic system can reproduce the behavior of silica-like glass formers is a question of great interest, both conceptual and for technological applications. We present a molecular-dynamics simulation of a simple monatomic system based on a metallic-like pair potential. We demonstrate that, while remaining stable with respect to crystallization, the system performs under cooling a first order phase transition from a fragile to an extremely strong liquid state. The low-temperature liquid phase can be cooled to a state of very high viscosity and low diffusivity while remaining in equilibrium. This result may provide a significant insight into the formation mechanisms of metallic glasses.
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| 8. |
- Elenius, Måns, 1974-
(författare)
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Computer Simulations of Simple Liquids with Tetrahedral Local Order : the Supercooled Liquid, Solids and Phase Transitions
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The understanding of complex condensed matter systems is an area of intense study. In this thesis, some properties of simple liquids with strong preference for tetrahedral local ordering are explored. These liquids are amenable to supercooling, and give complex crystalline structures on eventual crystallisation. All liquids studied are simple, monatomic and are similar to real metallic liquids. The vibrational density of states of a glass created in simulation is calculated. We show a correspondence between the vibrational properties of the crystal and the glass, indicating that the vibrational spectra of crystals can be used to understand the more complex vibrational spectra of the glass of the same substance. The dynamics of supercooled liquids is investigated using a previously not implemented comprehensive measure of structural relaxation. This new measure decays more slowly in the deeply supercooled domain than the commonly used measure. A new atomic model for octagonal quasicrystals is presented. The model is based on findings from a molecular dynamics simulation that resulted in 45˚ twinned β-Mn. A decoration is derived from the β-Mn unit cell and the unit cell of the intermediate structure found at the twinning interface. Extensive simulations are used to explore the phase diagram of a liquid at low densities. The resulting phase diagram shows a spinodal line and a phase coexistence region between a liquid and a crystalline phase ending in a critical point. This contradicts the old conclusion of the Landau theory -- that continuous transitions between liquids and crystals cannot exist The same liquid is explored at higher densities. Upon cooling the liquid performs a first order liquid-liquid phase transition. The low temperature liquid is shown to be strong and to have very good glass forming abilities. This result offers new insights into fragile to strong transitions and suggests the possibility of a good metallic glass former.
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| 9. |
- Elenius, Måns, 1974-, et al.
(författare)
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Evidence for a liquid-solid critical point in a simple monatomic system
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:104502
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Tidskriftsartikel (refereegranskat)abstract
- It is commonly believed that the transition line separating a liquid and a solid cannot be interrupted by a critical point. This opinion is based on the traditional symmetry argument that an isotropic liquid cannot be continuously transformed into a crystal with a discrete rotational and translational symmetry. We present here a molecular-dynamics simulation of a simple monatomic system suggesting the existence of a liquid-solid spinodal terminating at a critical point. We show that, in the critical region, the isotropic liquid continuously transforms into a phase with a mesoscopic order similar to that of the smectic liquid crystals. We argue that the existence of both the spinodal and the critical point can be explained by the close structural proximity between the mesophase and the crystal. This indicates a possibility of finding a similar thermodynamic behaviour in gelating colloids, liquid crystals and polymers.
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| 10. |
- Elenius, Måns, et al.
(författare)
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Evidence for a simple monatomic ideal glass former : The thermodynamic glass transition from a stable liquid phase
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:17, s. 174502-
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Tidskriftsartikel (refereegranskat)abstract
- Under cooling, a liquid can undergo a transition to the glassy state either as a result of a continuous slowing down or by a first-order polyamorphous phase transition. The second scenario has so far always been observed in a metastable liquid domain below the melting point where crystalline nucleation interfered with the glass formation. We report the first observation of the liquid-glass transition by a first-order polyamorphous phase transition from the equilibrium stable liquid phase. The observation was made in a molecular dynamics simulation of a one-component system with a model metallic pair potential. In this way, the model, demonstrating the thermodynamic glass transition from a stable liquid phase, may be regarded as a candidate for a simple monatomic ideal glass former. This observation is of conceptual importance in the context of continuing attempts to resolve the long-standing Kauzmann paradox. The possibility of a thermodynamic glass transition from an equilibrium melt in a metallic system also indicates a new strategy for the development of bulk metallic glass-forming alloys.
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