Time-dependent density functional theory for calculating the absorption spectra of metallic nanoclusters: feasibility and reliability, Recent Research Developments in Chemical Physics (original) (raw)
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The charging kinetics of electric double layers (EDLs) is closely related to the performance of a wide variety of nanostructured devices including supercapacitors, electro-actuators, and electrolyte-gated transistors. While room temperature ionic liquids (RTIL) are often used as the charge carrier in these new applications, the theoretical analyses are mostly based on conventional electrokinetic theories suitable for macroscopic electrochemical phenomena in aqueous solutions. In this work, we study the charging behavior of RTIL-EDLs using a coarse-grained molecular model and constant-potential molecular dynamics (MD) simulations. In stark contrast to the predictions of conventional theories, the MD results show oscillatory variations of ionic distributions and electrochemical properties in response to the separation between electrodes. The rate of EDL charging exhibits non-monotonic behavior revealing strong electrostatic correlations in RTIL under confinement. Recent experimental investigations of EDLC have Nano Research 2015, 8(3): 931-940
ACS Nano, 2012
The nanoscale interactions of room temperature ionic liquids (RTILs) at uncharged (graphene) and charged (muscovite mica) solid surfaces were evaluated with high resolution X-ray interface scattering and fully atomistic molecular dynamics simulations. At uncharged graphene surfaces, the imidazoliumbased RTIL ([bmim þ ][Tf 2 N À ]) exhibits a mixed cation/anion layering with a strong interfacial densification of the first RTIL layer. The first layer density observed via experiment is larger than that predicted by simulation and the apparent discrepancy can be understood with the inclusion of, dominantly, image charge and π-stacking interactions between the RTIL and the graphene sheet. In contrast, the RTIL structure adjacent to the charged mica surface exhibits an alternating cationÀanion layering extending 3.5 nm into the bulk fluid. The associated charge density profile demonstrates a pronounced charge overscreening (i.e., excess first-layer counterions with respect to the adjacent surface charge), highlighting the critical role of charge-induced nanoscale correlations of the RTIL. These observations confirm key aspects of a predicted electric double layer structure from an analytical LandauÀGinzburg-type continuum theory incorporating ion correlation effects, and provide a new baseline for understanding the fundamental nanoscale response of RTILs at charged interfaces.
The Journal of Physical Chemistry C, 2014
We designed a coarse-grained model for aromatic ionic liquids [CnM IM + [T f2N − ] with cations containing different alkyl groups. Within the framework of correlation-corrected density functional theory, the interfacial structure of studied ionic liquids are compared over a range of surface charge densities, alkyl chain lengths and surface geometries. The nonpolar hydrocarbon chains on cation tend to stretch out on the neutral surface. Differential capacitance of electric double layer formed by ionic liquids is explored with respect to surface electric potential. Comparison of ionic liquids model adjacent to planar, cylindrical and spherical surfaces confirms that higher and flatter differential capacitance curve is attributed to larger curvature of the surface. The influence of lengthening cation's alkyl chain on electrochemical properties is examined as well.
Density Functional Study of Charge Transfer at the Graphene/Ionic Liquid Interface
The Journal of Physical Chemistry C, 2018
We use density functional theory to analyze the charge transfer between lithium or magnesium cations and a graphene wall beyond the predictions of classical Marcus theory. To that end, metal atoms are placed in three different kinds of environments: (i) in a vacuum, (ii) among fluorine atoms to simulate a molten salt, and (iii) in an ionic liquid. We prove that a complete charge transfer to the electrodes takes place in all of the studied environments and that the charge transfer process starts at longer distances from the electrode in the ionic liquid. Vertical ionization potentials and vertical electron affinities are studied, and they confirm that the nanoconfined region close to the electrode is a favorable environment for electronic exchange. No significant difference between monovalent and divalent cations was found. Our results suggest a certain catalyzing effect of ionic liquids regarding metal-electrode charge transfer in these densely ionic environments. Moreover, they show that ionic liquids can actually enhance charge transfer to electrodes in electrochemical devices without significantly altering the nature of the process.
A classical density functional theory for interfacial layering of ionic liquids
Soft Matter, 2011
Ionic liquids have attracted much recent theoretical interest for broad applications as environmentallyfriendly solvents in separation and electrochemical processes. Because of the intrinsic complexity of organic ions and strong electrostatic correlations, the electrochemical properties of ionic liquids often defy the descriptions of conventional mean-field methods including the venerable, and over-used, Gouy-Chapman-Stern (GCS) theory. Classical density functional theory (DFT) has proven to be useful in previous studies of the electrostatic properties of aqueous electrolytes but until recently it has not been applied to ionic liquids. Here we report predictions from the DFT on the interfacial properties of ionic liquids near neutral or charged surfaces. By considering the molecular size, topology, and electrostatic correlations, we have examined major factors responsible for the unique features of electric-double layers of ionic-liquid including formation of long-range and alternating structures of cations and anions at charged surfaces.
Journal of Physics: Condensed Matter, 2016
The ongoing scientific interest in the properties and structure of electric double layers (EDLs) stems from their pivotal role in (super)capacitive energy storage, energy harvesting, and water treatment technologies. Classical density functional theory (DFT) is a promising framework for the study of the in-and out-of-plane structural properties of double layers. Supported by molecular dynamics simulations, we demonstrate the adequate performance of DFT for analyzing charge layering in the EDL perpendicular to the electrodes. We discuss charge storage and capacitance of the EDL and the impact of screening due to dielectric solvents. We further calculate, for the first time, the in-plane structure of the EDL within the framework of DFT. While our out-of-plane results already hint at structural in-plane transitions inside the EDL, which have been observed recently in simulations and experiments, our DFT approach performs poorly in predicting in-plane structure in comparison to simulations. However, our findings isolate fundamental issues in the theoretical description of the EDL within the primitive model and point towards limitations in the performance of DFT in describing the out-of-plane structure of the EDL at high concentrations and potentials.
Double layer in ionic liquids: capacitance vs. temperature from atomistic simulations
2022
In this study, we investigated the graphene-ionic liquid (EMImBF4) interface to clarify the effects of ambient temperature and potential on the differential capacitance. We complemented molecular dynamics simulations with density functional theory calculations to unravel the electrolyte and electrode contributions to the differential capacitance. As a result, we show: (1) the relation of characteristic saddle points of the capacitance-potential curve to the structural changes; (2) the smearing effect of temperature on the local structure and, consequently, on the capacitance; (3) rationalization of these observations with the interfacial bilayer model; and, finally, (4) how quantum capacitance correction dampens the influence of temperature and improves the agreement with the experimental data. These insights are of fundamental and practical importance for the application of similar interfaces in electrochemical energy storage and transformation devices, such as capacitors and actua...