Simulations of Ionic Liquids, Solutions, and Surfaces

Lynden‐Bell, R. M.; Pópolo, Mario G. Del; Youngs, Tristan G. A.; Kohanoff, Jorge; Hanke, C. G.; Harper, Jason B.; Pinilla, Carlos

doi:10.1021/ar700065s

Cited by 266 publications

(257 citation statements)

References 26 publications

(50 reference statements)

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“…Computer simulations involving ionic liquids at the molecular scale employ either the molecular dynamics (MD) or Monte-Carlo (MC) method 42 . In both cases, it is necessary to determine the intramolecular and intermolecular interactions at each step of the simulation.…”

Section: Methodsmentioning

confidence: 99%

Computer simulations of ionic liquids at electrochemical interfaces

Merlet¹,

Rotenberg²,

Madden³

et al. 2013

Phys. Chem. Chem. Phys.

154

188

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Ionic liquids are widely used as electrolytes in electrochemical devices. In this context, many experimental and theoretical approaches have been recently developed for characterizing their interface with electrodes. In this perspective article, we review the most recent advances in the field of computer simulations (mainly molecular dynamics). A methodology for simulating electrodes at constant electrical potential is presented. Several types of electrode geometries have been investigated by many groups, in order to model planar, corrugated and porous materials and we summarize the results obtained in terms of the structure of the liquids. This structure governs the quantity of charge which can be stored at the surface of the electrode for a given applied potential, which is the relevant quantity for the highly topical use of ionic liquids in supercapacitors (also known as electrochemical double-layer capacitors). A key feature, which was also shown by atomic force microscopy and surface force apparatus experiments, is the formation of a layered structure for all ionic liquids at the surface of planar electrodes. This organization cannot take place inside nanoporous electrodes, which results in a much better performance for the latter in supercapacitors. The agreement between simulations and electrochemical experiments remains qualitative only though, and we outline future directions which should enhance the predictive power of computer simulations. In the longer term, atomistic simulations will also be applied to the case of electron transfer reactions at the interface, enabling the application to a broader area of problems in electrochemistry, and the few recent works in this field are also commented upon.

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Section: Methodsmentioning

confidence: 99%

Computer simulations of ionic liquids at electrochemical interfaces

Merlet¹,

Rotenberg²,

Madden³

et al. 2013

Phys. Chem. Chem. Phys.

154

188

View full text Add to dashboard Cite

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“…where exchange is still treated at a semi-local level (GGA), while the semi-local component of the correlation is included in the new, fully non-local functional (2). The choice of the exchange GGA requires some care.…”

Section: A the Van Der Waals Functionalmentioning

confidence: 99%

“…The origin of this is the double integral in Eq. (2). Even if the distance |r − r | is truncated beyond a reasonable cutoff r c ≈ 15 Å, and if order-N techniques are used for systems of size larger than 2r c , the direct calculation of the double integral remains a formidable task, at least ten times more expensive than the LDA or the GGA.…”

Section: B Implementationmentioning

confidence: 99%

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Dispersion interactions in room-temperature ionic liquids: Results from a non-empirical density functional

Kohanoff¹,

Pinilla

Youngs

et al. 2011

The Journal of Chemical Physics

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The role of dispersion or van de Waals (VDW) interactions in imidazolium-based room-temperature ionic liquids is studied within the framework of density functional theory, using (2009)]. We present results for the equilibrium structure and lattice parameters of several crystalline phases, finding a general improvement with respect to both the local density (LDA) and the generalized gradient approximations (GGA). Similar to other systems characterized by VDW bonding, such as rare gas and benzene dimers as well as solid argon, equilibrium distances and volumes are consistently overestimated by ≈7%, compared to −11% within LDA and 11% within GGA. The intramolecular geometries are retained, while the intermolecular distances and orientations are significantly improved relative to LDA and GGA. The quality is superior to that achieved with tailor-made empirical VDW corrections ad hoc [M. G. Del Pópolo, C. Pinilla, and P. Ballone, J. Chem. Phys. 126, 144705 (2007)

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“…This includes a large number of fully atomistic simulations of ILs, which first appeared some ten years ago (Hanke et al , 2001;Lynden-Bell , 2010;Lynden-Bell et al , 2007). These reports have provided IL researchers with valuable physical and chemical information with which to rationalize many experimental observations.…”

Section: Introductionmentioning

confidence: 99%

A Classical Density Functional Theory of Ionic Liquids

2011

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Classical Density Functional Theory of Ionic Liquids 3 Other approachesILs are fascinating from a theoretical standpoint. In order to treat ILs, a theory must account for both electrostatic and steric correlations. Attempts to develop such a theory have appeared in the literature. These include the lattice based model by Kornyshev and co-workers (Fedorov et al. , 2008;Kornyshev , 2007). In another lattice approach by Lauw and coworkers (Lauw et al. , 2009), both cations and anions were modelled by a star-like architecture, with each monomer subject to an independently specified dielectric response. Under certain circumstances, these models were able to qualitatively reproduce the so-called "camel-shaped" differential capacitance, C D , profile observed in imidazolium ILs at carbon electrodes (Islam et al. , 2009;Lockett et al. , 2008a). This behaviour is an indication of subtle structuring effects at charged surfaces and is a stern test for theory. Although camel-shaped C D profiles are predicted, qualitative discrepancy against experimental results remains. This is not surprising since these crude theories lack a proper description of electrostatic correlations despite accounting for steric contributions. Charge-charge correlations have been shown to be important in interfacial phenomena of highly coupled electrostatic fluids. As with dispersion forces, ionic correlations are always attractive and lower the total energy. Thus, we expect that they will also play a role in establishing the camel shape of the C D . That this is the case, is seen from both simulations (Lamperski & Zydor , 2007;Vatamanu et al. , 2010) (Fedorov et al. , 2010;Trulsson et al. , 2010), play an important role in determining their properties. In this work, we will use a model for ILs wherein the molecular ions interact via dispersion, as well as electrostatic, forces and the cation has an oligomeric structure consistent with imidazolium ions. This model has also been adopted by us in previous recent publications (Forsman et al. , 2011;Trulsson et al. , 2010), and employs the methods of polymer free energy density functional theory (DFT) (Woodward , 1991). The result will be a simple, albeit approximate DFT for ILs. We have already introduced the salient features of the theory in a previous publication (Forsman et al. , 2011). Here, we will present a much more thorough treatment, emphasizing the relation to theories of simpler fluids. We will also extend the scope of the study with some emphasis on temperature dependence and the effects of ion-specific adsorption. The IL-DFT that we will discuss here is an off-lattice theory, whose accuracy can be straightforwardly tested against computer simulations of the same molecular model. We will begin with a discussion of relevant earlier work, in order to introduce the essential mechanistic components that will be combined in our density functional theory for ionic liquids. Classical density functional theory (DFT) of simple fluidsThe ideal gas law is known and used by most physicists and chemist...

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Simulations of Ionic Liquids, Solutions, and Surfaces

Cited by 266 publications

References 26 publications

Computer simulations of ionic liquids at electrochemical interfaces

Computer simulations of ionic liquids at electrochemical interfaces

Dispersion interactions in room-temperature ionic liquids: Results from a non-empirical density functional

A Classical Density Functional Theory of Ionic Liquids

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