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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 15 (1993), S. 541-546 
    ISSN: 0392-6737
    Keywords: Surface magnetism ; Classical spin models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present a mean-field study of the layer magnetization of a semi-infinite Ising model with intra-surfaceJ B and surface-bulkJ 1 interaction modified with respect to the bulk exchange interactionJ. This allows to discuss the extent of the spatial inhomogeneity perpendicular to a free surface. By following the magnetization of each layer, we are able to see how the critical exponents evolve from the bulk to the surface values. Furthermore, we introduce a new characteristic temperature,T em, where the surface magnetization departs from the bulk behaviour, as a possible candidate for the experimental determination ofJ 8 andJ 1.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 619-632 
    ISSN: 0392-6737
    Keywords: Kinetic and transport theory ; Classical, semiclassical and quantum theories of liquid structures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si discutono gli sviluppi di modelli di forze interatomiche appropriati agli stati liquido e amorfo di sistemi covalenti, con le caratteristiche di direzionalità provenienti dal legame chimico. In particolare, opportuni potenziali a tre corpi sono stati ampiamente usati, a partire dal lavoro di Stillinger e Weber sul silicio e mediante tecniche di simulazione numerica, per lo studio della struttura liquida e amorfa degli elementi semiconduttori del IV gruppo e dei loro calcogenuri binari. Tuttavia, modelli descritti in termini di potenziali di coppia appropriati, che possano tener conto, seppur ad un livello primitivo, degli effetti principali di dipendenze angolari nelle forze interatomiche efficaci, hanno interesse in relazione alla teoria meccanico-statistica dello stato liquido. In quest'ambito si dà particolare attenzione a modelli che usano particelle di legame per trattare la struttura di stati disordinati del germanio. Si discute anche la connessione tra la struttura liquida in un tale modello e un processo di cristillazizzazione accompagnato da localizzazione elettronica e da espansione di volume, quale si osserva in semiconduttori dei gruppi IV e III–V.
    Abstract: Резюме В последние несколъко лет предпринятЫ значителънЫе усилия для равития моделей межатомнЫх сил с целъю объяснения направленности связей при расчетах структурЫ жидкого и аморфного состояний. Модели, включаюше трехчастичнЫе потенциалЫ, явлются особенно удобнЫми для численного моделирования жидкого и аморфного состояний в злементарнЫх полупроводниках и бинарнЫх халчкогенидах злементов IV-группЫ, начиная с раборЫ Стилингера и Вебера на кремнии. Однако, модели парного потениала, котрЫе могут еше объяснитъ главнЫе зффектЫ угловЫх зависимотей зффективнЫх межатомнЫх сил, хотя на примитивном уровне, бЫли бЫ желателънЫ с точки зрения теории структурЫ жидкости. Предлается краткий обзор этих подходов, причем особое внимание уделяется моделям связаннЫх частиц, для структурЫ жидкого и аморфного германия. МЫ также обсуждаем соотношение между структурой жидкости в модели связаннЫх частиц и кристаллизацией, которая сопровождается увеличечнием обьма, которое наблюдается в злементарнЫх и полярнЫх III–V полупроводникх.
    Notes: Summary Considerable effort has been given for some years to developing models of interatomic forces aimed at accounting for bond directionality in liquid and amorphous state calculations. Models involving three-body potentials have been especially useful for computer simulation studies of liquid and amorphous states in elemental semiconductors and binary chalcogenides of group-IV elements, starting with the work of Stillinger and Weber on silicon. However, pair potential models that may still account for the main effects of angular dependences of the effective interatomic forces, though at a primitive level, are desirable from the viewpoint of liquid structure theory. Developments in this direction are briefly reviewed, with particular emphasis on bond particle models for the structure of liquid and amorphous germanium. We also discuss the relation between liquid structure in a bond-particle model and crystallization accompanied by electron localization and volume expansion, as observed in elemental and III-V polar semiconductors.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 11324-11335 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single particle dynamics of water confined in a nanopore is studied through computer molecular dynamics. The pore is modeled to represent the average properties of a pore of Vycor glass. Dynamics is analyzed at different hydration levels and upon supercooling. At all hydration levels and all temperatures investigated a layering effect is observed due to the strong hydrophilicity of the substrate. The time density correlators show, already at ambient temperature, strong deviations from the Debye and the stretched exponential behavior. Both on decreasing hydration level and upon supercooling we find features that can be related to the cage effect typical of a supercooled liquid undergoing a kinetic glass transition. Nonetheless the behavior predicted by mode coupling theory can be observed only by carrying out a proper shell analysis of the density correlators. Water molecules within the first two layers from the substrate are in a glassy state already at ambient temperature (bound water). The remaining subset of molecules (free water) undergoes a kinetic glass transition; the relaxation of the density correlators agree with the main predictions of the theory. From our data we can predict the temperature of structural arrest of free water. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 342-346 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular dynamics simulation of the microscopic structure of water confined in a silica pore is presented. A single cavity in the silica glass has been modeled as to reproduce the main features of the pores of real Vycor glass. A layer analysis of the site–site radial distribution functions evidences the presence in the pore of two subsets of water molecules with different microscopic structure. Molecules which reside in the inner layer, close to the center of the pore, have the same structure as bulk water but at a temperature of 30 K higher. On the contrary the structure of the water molecules in the outer layer, close to the substrate, is strongly influenced by the water–substrate hydrophilic interaction and sensible distortions of the H-bond network and of the orientational correlations between neighboring molecules show up. Lowering the hydration has little effect on the structure of water in the outer layer. The consequences on experimental determinations of the structural properties of water in confinement are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica B+C 111 (1981), S. 11-23 
    ISSN: 0378-4363
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Computer Physics Communications 60 (1990), S. 311-318 
    ISSN: 0010-4655
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9859-9867 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular dynamics simulation of water confined in a silica pore is performed in order to compare it with recent experimental results on water confined in porous Vycor glass at room temperature. A cylindrical pore of 40 Å is created inside a vitreous SiO2 cell, obtained by computer simulation. The resulting cavity offers water a rough hydrophilic surface and its geometry and size are similar to those of a typical pore in porous Vycor glass. The site-site distribution functions of water inside the pore are evaluated and compared with bulk water results. We find that the modifications of the site-site distribution functions, induced by confinement, are in qualitative agreement with the recent neutron diffraction experiment, confirming that the disturbance to the microscopic structure of water mainly concerns orientational arrangement of neighboring molecules. A layer analysis of MD results indicates that, while the geometrical constraint gives an almost constant density profile up to the layers closest to the interface, with a uniform average number of hydrogen bonds (HB), the hydrophilic interaction produces the wetting of the pore surface at the expenses of the adjacent water layers. Moreover, the orientational disorder together with a reduction of the average number of HB persists in the layers close to the interface, while water molecules cluster in the middle of the pore at a density and with a coordination similar to bulk water. © 1998 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Solid State Communications 19 (1976), S. 887-890 
    ISSN: 0038-1098
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Solid State Communications 55 (1985), S. 1109-1111 
    ISSN: 0038-1098
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 90 (1993), S. 215-228 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The finite-size scaling analysis of the density distribution function of subsystems of a system studied at constant total density is studied by a comparative investigation of two models: (i) the nearest-neighbor lattice gas model on the square lattice, choosing a total lattice size of 64×64 sites. (ii) The two-dimensional off-lattice Lennard-Jones system (truncated at a distance of 2.5 σ, σ being the range parameter of the interaction) withN=4096 particles, applying the NVT ensemble. In both models, the density distribution functionP L (ρ) is obtained forL×L subsystems for a wide range of temperaturesT, subblock linear dimensionsL and average densities 〈ρ〉. Particular attention is paid to the question whether accurate estimates of critical temperatureT c and critical density ρ c can be obtained. In the lattice gas model these critical parameters are known exactly and the limitations of the approach can thus be definitively asserted. The final estimates for the Lennard Jones problem areT c =0.47±0.01 (in units of the Lennard Jones energy ε) and ρ c (in units of σ2), a comparison with previous estimates is made.
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