Including many-body effects in models for ionic liquids

Abstract

Realistic modeling of ionic systems necessitates taking explicitly account of many-body effects. In molecular dynamics simulations, it is possible to introduce explicitly these effects through the use of additional degrees of freedom. Here we present two models: The first one only includes dipole polarization effect, while the second also accounts for quadrupole polarization as well as the effects of compression and deformation of an ion by its immediate coordination environment. All the parameters involved in these models are extracted from first-principles density functional theory calculations. This step is routinely done through an extended force-matching procedure, which has proven to be very succesfull for molten oxides and molten fluorides. Recent developments based on the use of localized orbitals can be used to complement the force-matching procedure by allowing for the direct calculations of several parameters such as the individual polarizabilities.

Evidence of dynamical local scale distribution heterogeneities in CsF-AF (A=Li, Na, K and Rb) molten salts

“…67 In addition, the accuracy of the molecular dynamics simulations necessitates taking account the ion polarizability. 69,70,71 In molten fluorides, the variations of the cations chemical shift have often provided crucial and more sensitive information to understand the local structure of the melt. 58,40,72 For this purpose, the chemical shift is measured for several crystalline compounds which structure is perfectly defined.…”

“…Indeed, the difference in the properties (size, polarizability) between cesium and lithium ions is much greater than the one between potassium and lithium ions. 83,69 Furthermore, the evidence of these effects must be higher at low The High Temperature NMR (HT NMR) spectra were recorded using a Bruker Avance WB 400MHz spectrometer, operating at 9.40 T. In situ HT NMR spectra were obtained by using the CO 2 laser heating system developed at CEMHTI-CNRS in Orléans (France) and previously described. 91,92 The samples were heated directly up to melts and the spectra were collected about 10 to 20K above respective liquidus temperature for each composition.…”

Shortcomings of the standard Lennard–Jones dispersion term in water models, studied with force matching

“…Among the several types of damping functions present in the literature, [20][21][22][23]28 we will make use of two of the most employed. 14,20,[23][24][25][26][27][30][31][32] The first one is a Fermilike (FE) function 23,46 f…”

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

“…An important proviso is that a constant oxide ion size cannot be assumed. Instead, the oxide ion environment has a profound influence as evidenced by the instability of these ions in the gas phase but their omnipresence in condensed matter (13,14). This variability was recognized in the construction of well-known tables of ionic radii (15, 16), although a constant size was assumed for a given oxide ion coordination number.…”

“…This variability was recognized in the construction of well-known tables of ionic radii (15,16), although a constant size was assumed for a given oxide ion coordination number. The variability of the oxide ion size is also a key theme in the development of transferable aspherical ion models which have been successful in accounting for many of the structure-related properties of oxide materials (13,14). In the following we use an empirical approach to tackle this oxygen size issue which leads, for example, to accurate packing fractions for the rutile-type structures of SiO 2 and GeO 2 (SI Text, section 2).…”