Combining Rare Events Techniques: Phase Change in Si Nanoparticles

We compare dynamical nonequilibrium molecular dynamics and continuum simulations of the dynamics of relaxation of a fluid system characterized by a non-uniform density profile. Results match quite well as long as the lengthscale of density nonuniformities are greater than the molecular scale (~10 times the molecular size). In presence of molecular scale features some of the continuum fields (e.g., density and momentum) are in good agreement with atomistic counterparts, but are smoother. On the contrary, other fields, such as the temperature field, present very large difference with respect to reference (atomistic) ones. This is due to the limited accuracy of some of the empirical relations used in continuum models, the equation of state of the fluid in the present example.

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“…Eq. 5 is recovered in the limit βk α → ∞, in which [7,8,10,11,18], proving that RMD samples the desired conditional PDF.…”

Section: A "Ab Initio" Hydrodynamicsmentioning

confidence: 91%

Relaxation of a steep density gradient in a simple fluid: Comparison between atomistic and continuum modeling

Pourali

Meloni

Magaletti

et al. 2014

The Journal of Chemical Physics

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“…Then, we plot the histogram of N sI and N sII at these two states along the nucleation process. To sample the conditional distribution mentioned above, we use restrained MD, 43 of which are provided in Ref. 25.…”

Section: Application To Biased Md: the Challenge Of Methane-hydrate Nmentioning

confidence: 99%

Clathrate structure-type recognition: Application to hydrate nucleation and crystallisation

Lauricella

Meloni

Liang

et al. 2015

The Journal of Chemical Physics

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For clathrate-hydrate polymorphic structure-type (sI versus sII), geometric recognition criteria have been developed and validated. These are applied to the study of the rich interplay and development of both sI and sII motifs in a variety of hydrate-nucleation events for methane and H2S hydrate studied by direct and enhanced-sampling molecular dynamics (MD) simulations. In the case of nucleation of methane hydrate from enhanced-sampling simulation, we notice that already at the transition state, ∼80% of the enclathrated CH4 molecules are contained in a well-structured (sII) clathrate-like crystallite. For direct MD simulation of nucleation of H2S hydrate, some sI/sII polymorphic diversity was encountered, and it was found that a realistic dissipation of the nucleation energy (in view of non-equilibrium relaxation to either microcanonical (NVE) or isothermal-isobaric (NPT) distributions) is important to determine the relative propensity to form sI versus sII motifs.

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“…The presence of hysteresis in liquid porosimetry experiments, in which one controls the volume of the cylinder-piston system, suggests that the volume of the liquid in the cavity is an insufficient descriptor of the process. Indeed, hysteresis is connected to multiple attractive basins in the space orthogonal to the variable controlled [18,40,41], here the volume of the computational sample. In this section, we describe continuum calculations and atomistic simulations that brought us to identify a suitable descriptor for intrusion/extrusion.…”

Section: Descriptors Of Intrusion and Extrusionmentioning

confidence: 99%

Liquid intrusion in and extrusion from non-wettable nanopores for technological applications

et al. 2021

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In this article, we review some recent theoretical results about intrusion and extrusion of non-wetting liquids in and out of cavities of nanotextured surfaces and nanoporous materials. Nanoscale confinement allows these processes to happen at conditions which significantly differ from bulk phase coexistence. In particular, the pressure at which a liquid penetrates in and exits from cavities is of interest for many technological applications such as energy storage, dissipation, and conversion, materials with negative compressibility, ion channels, liquid chromatography, and more. Notwithstanding its technological interest, intrusion/extrusion processes are difficult to understand and control solely via experiments: the missing step is often a simple theory capable of providing a microscopic interpretation of the results, e.g., of liquid porosimetry or other techniques used in the field, especially in the case of complex nanoporous media. In this context, simulations can help shedding light on the relation between the morphology of pores, the chemical composition of the solids and liquids, and the thermodynamics and kinetics of intrusion and extrusion. Indeed, the intrusion/extrusion kinetics is determined by the presence of free energy barriers and special approaches, the so-called rare event techniques, must be used to study these processes. Usually, rare event techniques are employed to investigate processes occurring in relatively simple molecular systems, while intrusion/extrusion concerns the collective dynamics of hundreds to thousands of degrees of freedom, the molecules of a liquid entering in or exiting from a cavity, which, from the methodological point of view, is itself a challenge.

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Combining Rare Events Techniques: Phase Change in Si Nanoparticles

Cited by 13 publications

References 41 publications

Relaxation of a steep density gradient in a simple fluid: Comparison between atomistic and continuum modeling

Relaxation of a steep density gradient in a simple fluid: Comparison between atomistic and continuum modeling

Clathrate structure-type recognition: Application to hydrate nucleation and crystallisation

Liquid intrusion in and extrusion from non-wettable nanopores for technological applications

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