Atomistic Mechanism of NaCl Nucleation from an Aqueous Solution

Zahn, Dirk

doi:10.1103/physrevlett.92.040801

Cited by 144 publications

(152 citation statements)

References 17 publications

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“…Such level of modeling, arguably most realistic, is computationally demanding, so a special technique was used to sample the phase space more efficiently. 24 Small ion clusters were observed that were interpreted as stable precursors of NaCl nanocrystals.…”

Section: Introductionmentioning

confidence: 99%

Microscopic mechanism of nanocrystal formation from solution by cluster aggregation and coalescence

Hassan

2011

The Journal of Chemical Physics

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Solute-cluster aggregation and particle fusion have recently been suggested as alternative routes to the classical mechanism of nucleation from solution. The role of both processes in the crystallization of an aqueous electrolyte under controlled salt addition is here elucidated by molecular dynamics simulation. The time scale of the simulation allows direct observation of the entire crystallization pathway, from early events in the prenucleation stage to the formation of a nanocrystal in equilibrium with concentrated solution. The precursor originates in a small amorphous aggregate stabilized by hydration forces. The core of the nucleus becomes crystalline over time and grows by coalescence of the amorphous phase deposited at the surface. Imperfections of ion packing during coalescence promote growth of two conjoint crystallites. A parameter of order and calculated cohesive energies reflect the increasing crystalline order and stress relief at the grain boundary. Cluster aggregation plays a major role both in the formation of the nucleus and in the early stages of postnucleation growth. The mechanism identified shares common features with nucleation of solids from the melt and of liquid droplets from the vapor.

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Section: Introductionmentioning

confidence: 99%

Microscopic mechanism of nanocrystal formation from solution by cluster aggregation and coalescence

Hassan

2011

The Journal of Chemical Physics

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“…In this regard, molecular simulations play an important role and much work has been devoted to the study of homogeneous nucleation in simple model systems like Lennard-Jones particles or hard spheres (1)(2)(3). More recently, growing attention has been paid to the computer simulation of nucleation from solution of organic and inorganic materials (4)(5)(6)(7)(8)(9)(10)(11).…”

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confidence: 99%

Molecular-dynamics simulations of urea nucleation from aqueous solution

Salvalaglio

Perego

Giberti

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

161

231

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Despite its ubiquitous character and relevance in many branches of science and engineering, nucleation from solution remains elusive. In this framework, molecular simulations represent a powerful tool to provide insight into nucleation at the molecular scale. In this work, we combine theory and molecular simulations to describe urea nucleation from aqueous solution. Taking advantage of well-tempered metadynamics, we compute the freeenergy change associated to the phase transition. We find that such a free-energy profile is characterized by significant finite-size effects that can, however, be accounted for. The description of the nucleation process emerging from our analysis differs from classical nucleation theory. Nucleation of crystal-like clusters is in fact preceded by large concentration fluctuations, indicating a predominant two-step process, whereby embryonic crystal nuclei emerge from dense, disordered urea clusters. Furthermore, in the early stages of nucleation, two different polymorphs are seen to compete.T he nucleation of crystals from solution plays an important role in a variety of chemical and engineering processes. However, the very small scale that characterizes the early stages of nucleation makes its experimental study rather challenging. In this regard, molecular simulations play an important role and much work has been devoted to the study of homogeneous nucleation in simple model systems like Lennard-Jones particles or hard spheres (1-3). More recently, growing attention has been paid to the computer simulation of nucleation from solution of organic and inorganic materials (4-11).However, these simulations have to face an important challenge. Nucleation is a typical example of a rare event occurring on a timescale that is much longer than what atomistic simulations can typically afford. The problem is most easily understood if we focus on molecular dynamics (MD), which is the sampling method used here but it plagues other methods as well. In MD, the shortest timescale to be used for a correct integration of the equation of motion is dictated by the fastest atomic motions such as vibrations or rotations. Due to this constraint in the integration step, present MD simulations can reach timescales up to microseconds unless specific hardware, accessible only to few, is used. Even in this case the scale of the accessible times can be stretched only to the milliseconds range, a far cry from the much longer scale of nucleation phenomena.These timescale limitations affect molecular simulations in several other research fields, such as ligand protein binding, protein folding, or slow chemical reactions, to name just a few. To overcome this limit, many enhanced sampling methods have been proposed (12-21). Several of them are based on the application of a suitable external bias potential (12-14) that speeds up configurational sampling and permits free energies to be evaluated and transition rates to be computed (22)(23)(24). Here, we shall use well-tempered (WT) metadynamics to enhance the nucleation...

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“…Interestingly, alteration of Lennard-Jones parameters has been used to initiate a nucleation process for NaCl that was subsequently investigated by using the path sampling method developed by Chandler and co-workers. 60 The authors modified the ion-water interactions to obtain an artificial system that crystallizes in a few tens of picoseconds. Hence, nucleation could be studied from simulations generated by using AMBER parameters.…”

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confidence: 99%

Spontaneous Formation of KCl Aggregates in Biomolecular Simulations: A Force Field Issue?

Auffinger

Cheatham

Vaiana

2007

J. Chem. Theory Comput.

162

177

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Realistic all-atom simulation of biological systems requires accurate modeling of both the biomolecules and their ionic environment. Recently, ion nucleation phenomena leading to the rapid growth of KCl or NaCl clusters in the vicinity of biomolecular systems have been reported. To better understand this phenomenon, molecular dynamics simulations of KCl aqueous solutions at three (1.0, 0.25, and 0.10 M) concentrations were performed. Two popular water models (TIP3P and SPC/E) and two Lennard-Jones parameter sets (AMBER and Dang) were combined to produce a total of 80 ns of molecular dynamics trajectories. Results suggest that the use of the Dang cation Lennard-Jones parameters instead of those adopted by the AMBER force-field produces a more accurate description of the ionic solution. In the later case, formation of salt aggregates is probably indicative of an artifact resulting from misbalanced force-field parameters. Because similar results were obtained with two different water parameter sets, the simulations exclude a water model dependency in the formation of anomalous ionic clusters. Overall, the results strongly suggest that for accurate modeling of ions in biomolecular systems, great care should be taken in choosing balanced ionic parameters even when using the most popular force-fields. These results invite a reexamination of older data obtained using available force-fields and a thorough check of the quality of current parameters sets by performing simulations at finite (>0.25 M) instead of minimal salt conditions.

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Atomistic Mechanism of NaCl Nucleation from an Aqueous Solution

Cited by 144 publications

References 17 publications

Microscopic mechanism of nanocrystal formation from solution by cluster aggregation and coalescence

Microscopic mechanism of nanocrystal formation from solution by cluster aggregation and coalescence

Molecular-dynamics simulations of urea nucleation from aqueous solution

Spontaneous Formation of KCl Aggregates in Biomolecular Simulations: A Force Field Issue?

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