223 research outputs found
Computer simulations of ionic liquids at electrochemical interfaces
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.Comment: 12 pages, 10 figures, perspective articl
Effect of dispersion interactions on the properties of LiF in condensed phases
Classical molecular dynamics simulations are performed on LiF in the
framework of the polarizable ion model. The overlap-repulsion and polarization
terms of the interaction potential are derived on a purely non empirical,
first-principles basis. For the dispersion, three cases are considered: a first
one in which the dispersion parameters are set to zero and two others in which
they are included, with different parameterizations. Various thermodynamic,
structural and dynamic properties are calculated for the solid and liquid
phases. The melting temperature is also obtained by direct coexistence
simulations of the liquid and solid phases. Dispersion interactions appear to
have an important effect on the density of both phases and on the melting
point, although the liquid properties are not affected when simulations are
performed in the NVT ensemble at the experimental density.Comment: 8 pages, 5 figure
A transferable ab-initio based force field for aqueous ions
We present a new polarizable force field for aqueous ions (Li+, Na+, K+, Rb+,
Cs+, Mg2+, Ca2+, Sr2+ and Cl-) derived from condensed phase ab-initio
calculations. We use Maximally Localized Wannier Functions together with a
generalized force and dipole-matching procedure to determine the whole set of
parameters. Experimental data is then used only for validation purposes and a
good agreement is obtained for structural, dynamic and thermodynamic
properties. The same procedure applied to crystalline phases allows to
parametrize the interaction between cations and the chloride anion. Finally, we
illustrate the good transferability of the force field to other thermodynamic
conditions by investigating concentrated solutions.Comment: 31 pages, 8 figure
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