Person: Montero De Hijes, Pablo
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First Name
Pablo
Last Name
Montero De Hijes
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Física
Area
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Item Homogeneous nucleation of NaCl in supersaturated solutions(Physical Chemistry Chemical Physics, 2021) Pulido Lamas, Cintia; Espinosa, Jorge; Conde, Maria; Ramirez, Jorge; Montero De Hijes, Pablo; Noya, Eva; Vega De Las Heras, Carlos; Sanz, EvaThe seeding method is an approximate approach to investigate nucleation that combines molecular dynamics simulations with classical nucleation theory. Recently, this technique has been successfully implemented in a broad range of nucleation studies. However, its accuracy is subject to the arbitrary choice of the order parameter threshold used to distinguish liquid-like from solid-like molecules. We revisit here the crystallization of NaCl from a supersaturated brine solution and show that consistency between seeding and rigorous methods, like Forward Flux Sampling (from previous work) or spontaneous crystallization (from this work), is achieved by following a mislabelling criterion to select such threshold (i.e. equaling the fraction of the mislabelled particles in the bulk parent and nucleating phases). This work supports the use of seeding to obtain fast and reasonably accurate nucleation rate estimates and the mislabelling criterion as one giving the relevant cluster size for classical nucleation theory in crystallization studiesItem Anomalous Behavior in the Nucleation of Ice at Negative Pressures(Physical Review Letters, 2021) Bianco, Valentino; Montero De Hijes, Pablo; Cintia P. Lamas; Sanz García, Eduardo Santiago; Carlos Vega; Vega De Las Heras, CarlosIce nucleation is a phenomenon that, despite the relevant implications for life, atmospheric sciences, and technological applications, is far from being completely understood, especially under extreme thermodynamic conditions. In this work we present a computational investigation of the homogeneous ice nucleation at negative pressures. By means of the seeding technique we estimate the size of the ice critical nucleus Nc for the TIP4P/Ice water model. This is done along the isotherms 230, 240, and 250 K, from positive to negative pressures until reaching the liquid-gas kinetic stability limit (where cavitation cannot be avoided). We find that Nc is nonmonotonic upon depressurization, reaching a minimum at negative pressures in the doubly metastable region of water. According to classical nucleation theory we establish the nucleation rate J and the surface tension γ, revealing a retracing behavior of both when the liquid-gas kinetic stability limit is approached. We also predict a reentrant behavior of the homogeneous nucleation line. The reentrance of these properties is related to the reentrance of the coexistence line at negative pressure, revealing new anomalies of water. The results of this work suggest the possibility of having metastable samples of liquid water for long times at negative pressure provided that heterogeneous nucleation is suppressed.Item Cinética de la cristalización(2022) Montero De Hijes, Pablo; Vega De Las Heras, Carlos; Sanz García, Eduardo SantiagoLa cristalización de un líquido consta de varias etapas, empezando por que éste se encuentre en condiciones de metaestabilidad. Por ejemplo, un caso típico es el de un líquido que se enfría más allá de su temperatura de coexistencia. Por lo tanto, la temperatura y la presión del mismo correspondan a la región cristalina en el diagrama de fases de la sustancia por lo que el cristal es la fase más estable y por lo tanto la que cabría esperar. Sin embargo, esta no es condicion suficiente para observar la transición de forma espontánea dado que se trata de un proceso activado que puede tomar un tiempo considerable en función de las condiciones termodinámicas 1. Este tipo de procesos se caracterizan por la transición entre estados separados por una barrera de energía. En este caso, dicha barrera se forma por la competición energética entre estabilidad termodinámica y la penalización de crear interfase sólido-líquido. La tensión interfacial es una variable clave en el proceso pues es la que se opone a la transición y da lugar a que el proceso sea activado logrando que un líquido metaestable pueda sobrevivir durante largo tiempo. Cuando la cristalización emerge en una sustancia pura el proceso se denomina nucleación homogénea mientras que en presencia de impurezas o sustratos, el proceso se denomina nucleación heterogénea. En ambos casos, son fluctuaciones de orden local las responsables del inicio de la transición pero mientras que en la nucleación homogénea ocurren en el seno del fluido, en la nucleación heterogénea ocurren también próximas a una intefase lo cual facilita la nucleación 24...Item Interfacial Free Energy and Tolman Length of Curved Liquid-Solid Interfaces from Equilibrium Studies(Journal of Physical Chemitry C, 2020) Montero De Hijes, Pablo; Espinosa, Jorge R.; Bianco, Valentino; Sanz García, Eduardo Santiago; Vega De Las Heras, CarlosIn this work, we study by means of simulations of hard spheres the equilibrium between a spherical solid cluster and the fluid. In the NVT ensemble we observe stable/metastable clusters of the solid phase in equilibrium with the fluid, representing configurations that are global/local minima of the Helmholtz free energy. Then, we run NpT simulations of the equilibrated system at the average pressure of the NVT run and observe that the clusters are critical because they grow/shrink with a probability of 1/2. Therefore, a crystal cluster equilibrated in the NVT ensemble corresponds to a Gibbs free energy máximum where the nucleus is in unstable equilibrium with the surrounding fluid, in accordance with what has been recently shown for vapor bubbles in equilibrium with the liquid. Then, within the Seeding framework, we use Classical Nucleation Theory to obtain both the interfacial free energy γ and the nucleation rate. The latter is in very good agreement with independent estimates using techniques that do not rely on Classical Nucleation Theory when the mislabeling criterion is used to identify the molecules of the solid cluster. We therefore argue that the radius obtained from the mislabeling criterion provides a good approximation for the radius of tension, R_s . We obtain an estimate of the Tolman length by extrapolating the difference between R e (the Gibbs dividing surface) and R s to infinite radius. We show that such definition of the Tolman length coincides with that obtained by fitting γ versus 1/R_s to a straight line as recently applied to hard spheres.Item Viscosity and self-diffusion of supercooled and stretched water from molecular dynamics simulations(Journal of chemical physics, 2018) Montero De Hijes, Pablo; Sanz García, Eduardo Santiago; Joly, Laurent; Valeriani, Chantal; Caupin, FredericAmong the numerous anomalies of water, the acceleration of dynamics under pressure is particularly puzzling. Whereas the diffusivity anomaly observed in experiments has been reproduced in several computer studies, the parallel viscosity anomaly has received less attention. Here we simulate viscosity and the self-diffusion coefficient of the TIP4P/2005 water model over a broad temperature and pressure range. We reproduce the experimental behavior and find additional anomalies at negative pressure. The anomalous effect of pressure on dynamic properties becomes more pronounced upon cooling, reaching two orders of magnitude for viscosity at 220 K. We analyze our results with a dynamic extension of a thermodynamic two-state model, an approach which has proved successful in describing experimental data. Water is regarded as a mixture of interconverting species with contrasting dynamic behaviors, one being strong (Arrhenius) and the other fragile (non-Arrhenius). The dynamic parameters of the two-state models are remarkably close between experiment and simulations. The larger pressure range accessible to simulations suggests a modification of the dynamic two-state model, which in turn also improves the agreement with experimental data. Furthermore, our simulations demonstrate the decoupling between viscosity eta and self-diffusion coefficient D as a function of temperature T. The Stokes-Einstein relation, which predicts a constant D eta/T, is violated when T is lowered, in connection with the Widom line defined by an equal fraction of the two interconverting species. These results provide a unifying picture of thermodynamics and dynamics in water and call for experiments at negative pressure. Published by AIP Publishing.