Molecular dynamics simulations of solutions at constant chemical potential

Perego, Claudio; Salvalaglio, Matteo; Parrinello, Michele

doi:10.1063/1.4917200

Cited by 81 publications

(133 citation statements)

References 40 publications

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“…Therefore, in practice, the AIMD setup for a biased interface must be subjected to additional serious limitations suiting the goals of simulations. For instance, the steady state regime at (or beyond) the redox potential may become inaccessible to AIMD as it would require simulations at constant chemical potential of ions 24 to replenish the lost ones, while the actual goal usually is to study the nascent "just forming" states resulting from irreversible ET.…”

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confidence: 99%

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

Baskin

2017

J. Electrochem. Soc.

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We develop a continuum theory of electrolyte solutions in contact with a metal electrode, based on a generalized free energy functional, and use it to explore the structure of the electric double layer at different electrochemical conditions. The model captures the effects of specific adsorption of ions and solvent polarization, and can be applied on the same footing to cases with non-zero faradaic current, beyond the classical double-layer regime. These advances permit the prediction of peculiar character in the ion profiles at electrode potentials near the redox level, exploration of the electrochemical stability of the interface, and differentiation between the mechanisms of electron and ion transport and associated time scales. The developed methodology enables us to selfconsistently determine the fundamental limits for a microscopic description of biased interfaces, in terms characteristic sizes and time scales of relevant processes, within atomistic and ab initio molecular dynamics simulations. As the efficiency of electrochemical conversion is dictated by the energetics of elementary charge transfer reactions occurring at the electrode/electrolyte interface, the formulation of methods of control over these reactions has become the pivotal goal of fundamental material science for advanced energy storage systems. The ultimate goal of theoretical electrochemistry then is to explore the energetics of the relevant processes from an atomistic perspective by means of ab initio molecular dynamics (AIMD) where ionic and electronic components of the system are described explicitly and are constrained by various realistic conditions, such as the external bias, the temperature and the electrolyte concentration. However, despite more than a decade of efforts this goal is still far from being fulfilled.There are several interconnected fundamental problems to resolve before an atomistic approach could be routinely used to describe electrochemistry, if only at the level of a half-cell (i.e., a single electrodeelectrolyte interface). First, there are at least three distinct regimes of performance of the electrochemical interface and each of these is characterized by different sets of the time and space scales: a) the classical electric double layer (EDL) regime when no charge transfer is assumed, b) the regime of an electrode at equilibrium with the electrolyte (open circuit conditions, (OCP)) when only an exchange current in a form of mutually compensating fluxes of charged particles is possible, and c) the "true" electrochemical regime with a non-zero net faradaic current. As long as the goal of atomistic simulations is to reach a state when one would observe the actual electrochemical reactions driven by the bias, the computational electrode potential scanning protocol should carry the system through a set of (quasi-)equilibrium points at which the atomistic structure is consistent with the targeted external conditions. The key requirement for such simulations is thus thermodynamic stability of the interface that encom...

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confidence: 99%

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

Baskin

2017

J. Electrochem. Soc.

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“…However, such size limitations are particularly dramatic in the simulation of phase transformations, such as crystal growth from solution or dissolution of crystals [13,[102][103][104][105]. While for a macroscopic system, the solutions' chemical potential does not change in the time scale accessible by MD simulation, the standard MD simulations cannot guarantee this.…”

Section: Constant Chemical Potentialmentioning

confidence: 99%

“…In MD, this should be handled by finite-size corrections. Recently, some works appeared, which discuss finite-size effects and methods to expand the information from MD simulations of phase transformations towards the limit of a macroscopic system [13,[102][103][104][105]. However, most of them consider only nucleation processes, where the correction term is introduced based on the classical nucleation theory and modified liquid drop model for describing nucleation in a finite closed model [102], sharing many approximations and shortcomings.…”

Section: Constant Chemical Potentialmentioning

confidence: 99%

“…Furthermore, insertions of particles near the growing crystal or insertion of fractional particles may lead to unphysical effects, which may ultimately obscure the true growth mechanisms and rates [106]. An approach to allow for simulations under constant chemical potential was proposed by Perego et al [105]. Their CµMD method allows to maintain a region containing the growing/dissolving crystal and its immediate surrounding at constant solution concentration, while the remainder of the simulation box acts as a molecular reservoir.…”

Section: Constant Chemical Potentialmentioning

confidence: 99%

“…The method was successfully applied to study planar crystal-solution interfaces. However, significant changes are needed to extend the method to other geometries [105]. Moreover, the parametrization of the CµMD method is not trivial and needs a preliminary tuning and testing to provide an effective decoupling between the reservoir region and the growing crystal [105].…”

Section: Constant Chemical Potentialmentioning

confidence: 99%

See 2 more Smart Citations

In Silico Prediction of Growth and Dissolution Rates for Organic Molecular Crystals: A Multiscale Approach

2017

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Solution crystallization and dissolution are of fundamental importance to science and industry alike and are key processes in the production of many pharmaceutical products, special chemicals, and so forth. The ability to predict crystal growth and dissolution rates from theory and simulation alone would be of a great benefit to science and industry but is greatly hindered by the molecular nature of the phenomenon. To study crystal growth or dissolution one needs a multiscale simulation approach, in which molecular-level behavior is used to parametrize methods capable of simulating up to the microscale and beyond, where the theoretical results would be industrially relevant and easily comparable to experimental results. Here, we review the recent progress made by our group in the elaboration of such multiscale approach for the prediction of growth and dissolution rates for organic crystals on the basis of molecular structure only and highlight the challenges and future directions of methodic development.

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Polymorphism of Syndiotactic Polystyrene Crystals from Multiscale Simulations

Лю

Kremer

Bereau

2018

Advcd Theory and Sims

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Syndiotactic polystyrene (sPS) exhibits complex polymorphic behavior upon crystallization. Computational modeling of polymer crystallization has remained a challenging task because the relevant processes are slow on the molecular time scale. A detailed characterization of sPS-crystal polymorphism by means of coarse-grained (CG) and atomistic (AA) modeling is reported herein. The CG model, parametrized in the melt, shows remarkable transferability properties in the crystalline phase. Not only is the transition temperature in good agreement with atomistic simulations, it stabilizes the main α and β polymorphs, observed experimentally. The propensities of polymorphs at the CG and AA levels are compared in detail, as well as finite-size and box-geometry effects. All in all, CG modeling stands as an efficient approach to characterize polymer-crystal poymorphism at large scale.in this work. The unit cells are projected onto the a − b plane, and the backbones of the chains are along the c axis. Experimentally, two types of crystalline phases have been identified: the zig-zag-chain forming α [12][13][14][15] and β [16,17] appear upon thermal annealing of a melt, whereas the other three helix-forming crystalline phases, γ , [18,19] δ, [20][21][22] and ε [23][24][25] are obtained by solution processing. The α and β forms of sPS are further classified into the limiting disordered forms (α and β ) and limiting ordered forms (α and β ). [12,14,16,26] In particular, melt crystallization procedures generally produce the limiting ordered α and limiting disordered β models. [26] The limiting disordered α model is obtained by annealing the amorphous sample, [26] whereas the limiting ordered β model is obtained by crystallization from solution, when the solvent is rapidly removed at higher temperatures above 150°C. [16] Two of the helical crystalline phases (δ and ε) can only be obtained by guest removal from co-crystalline phases. The δ e form is transformed into the solvent-free γ form by annealing above 130°C. [18,20,26] These findings illustrate that the experimentally observed structures depend on the experimental processing, making conclusions about their thermodynamic equilibrium difficult.Several molecular simulation studies have been performed to better understand the nanoporous cavity structures formed by crystalline sPS. Tamai and co-workers [27] studied the size, shape, and connectivity of the cavities in the crystal α, β, and δ forms. Some other properties were also studied, such as diffusion of gases, [28,29] reorientational motion of guest solvents, [30,31] and sorption of small molecules. [32][33][34] While these studies helped understand the behavior of specific forms of sPS crystals, they did not address the crystallization process or the relative stability of the polymorphs. By studying sPS on the nanosecond timescale, they could not observe self assembly and spontaneous polymorph interconversion, due to their metastability. Yamamoto observed the onset of isotactic polypropylene crystallization, but leading to a ...

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Molecular dynamics simulations of solutions at constant chemical potential

Cited by 81 publications

References 40 publications

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

In Silico Prediction of Growth and Dissolution Rates for Organic Molecular Crystals: A Multiscale Approach

Polymorphism of Syndiotactic Polystyrene Crystals from Multiscale Simulations

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