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Nucleation criteria detection as a mean to investigate metastable state
Celný, David ; Span, R. ; Vrabec, J.
Focus is given to the core problematic, reaching the nucleation region and sample the relevant data for selected pure substance. This termodynamic condition required for nucleation are found in so called metastable region. Metastable region is found between binodal and spinodal line separating it from the stable and unstable system condition respectively.\nObtaining the data in this area proves to be an experimental challenge, therefore the data has to be gathered using other means. Proposed setup relies two part approach combining equation of state (EoS) and molecular simulation. The computational core is done with molecular dynamics tool combined with on the fly performing decision cluster criterion utilized is already available in previously published work. These cluster criteria ensure that the system is only calculated within targeted conditions and the sampled micro-states remain valid observations. To capture whole metastable region two criteria are present for both cluster and void case as illustrated below. Remaining part utilize the equation of state for the initial system condition sampling of the metastable region by calculating the stability line and predicting the instability line for the LJ fluid as show in Linhart et.al. . These thermodynamic condition probes are evaluated afterwards with the established simulation method. Intermediate result from simulations are collected in form of both Helmholtz energy temperature and density derivatives descriptors as well as time averages of system properties for fluids like LJ, Oxygen and Nitrogen.
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Molecular Simulations of the Vapor–Liquid Phase Interfaces of Pure Water Modeled with the SPC/E and the TIP4P/2005 Molecular Models
Vinš, Václav ; Celný, David ; Planková, Barbora ; Němec, Tomáš ; Duška, Michal ; Hrubý, Jan
In our previous study [Planková et al., EPJWeb. Conf. 92, 02071 (2015)], several molecular simulations of vapor-liquid phase interfaces for pure water were performed using the DL POLY Classic software. The TIP4P/2005 molecular model was successfully used for the modeling of the density profile and the thickness of phase interfaces together with the temperature dependence of the surface tension. In the current study, the extended simple point charge (SPC/E) model for water together with TIP4P/2005 were employed for the investigation of vapor-liquid phase interfaces over a wide temperature range from 250 K to 600 K. Results of the new simulations are in a good agreement with most of the literature data. TIP4P/2005 provides better results for the saturated liquid density with its maximum close to 275 K, while SPC/E predicts slightly better saturated vapor density. Both models give qualitatively correct representation for the surface tension of water.
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Mathematical modeling of planar and spherical vapor–liquid phase interfaces for multicomponent fluids
Celný, David ; Vinš, Václav ; Planková, Barbora ; Hrubý, Jan
Methods for accurate modeling of phase interfaces are important for understanding natural processes and application in technology. In particular, prediction of the non-equilibrium phase transition requires the knowledge of the strongly curved phase interfaces of microscopic droplets. In our work, we focus on the spherical vapor–liquid interfaces for binary mixtures. We developed a computational method able to determine the density and concentration profiles. The fundamentals of our approach lie in the gradient theory, allowing to transcribe the functional formulation into a system of Euler-Langrange equations. System is then modified into a shape suitable for iterative computation. For this task, we employ the Newton-Raphson and the shooting methods ensuring a good convergence speed. For the thermodynamic properties, the PC–SAFT EoS is used. We determined the density and concentration profiles of the binary mixture C O 2 & C 9 H 20 for spherical phase interfaces at various saturation factors.
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