Characterization of the complex ion dynamics in lithium silicate glasses via computer simulations

We present results of molecular dynamics simulations on lithium metasilicate over a broad range of temperatures for which the silicate network is frozen in but the lithium ions can still be equilibrated. The lithium dynamics is studied via the analysis of different correlation functions. The activation energy for the lithium mobility agrees very well with experimental data. The correlation of the dynamics of adjacent ions is weak. At low temperatures the dynamics can be separated into local vibrational dynamics and hopping events between adjacent lithium sites. The derivative of the mean square displacement displays several characteristic time regimes. They can be directly mapped onto respective frequency regimes for the conductivity. In particular it is possible to identify time regimes dominated by localized dynamics and long-range dynamics, respectively. The question of time-temperature superposition is discussed for the mean square displacement and the incoherent scattering function.Comment: to be published in Phys. Chem. Chem. Phy

Structural characterization of an ionic liquid in bulk and in nano-confined environment using data from MD simulations

This article contains data on structural characterization of the [C2Mim][NTf2] in bulk and in nano-confined environment obtained using MD simulations. These data supplement those presented in the paper “Insights from Molecular Dynamics Simulations on Structural Organization and Diffusive Dynamics of an Ionic Liquid at Solid and Vacuum Interfaces” [1], where force fields with three different charge methods and three charge scaling factors were used for the analysis of the IL in the bulk, at the interface with the vacuum and the IL film in the contact with a hydroxylated alumina surface. Here, we present details on the construction of the model systems in an extended detailed methods section. Furthermore, for best parametrization, structural and dynamic properties of IL in different environment are studied with certain features presented herein

Theory of point defect energetics: A review

285-293The energetics of point defects provide the controlling factor in determining the atomistic mechanisms in a wide range of solid state processes. We present here a pedagogical overview of the development of the continuum, quasi-lattice and lattice theories for different classes of point defects and materials. Varied approaches were followed in the past in modelling the relevant perfect crystals for interatomic forces for nonionic solids and model potentials for ionic materials. The earliest continuum approaches are those of Eshelby and Jost for treating point defects as elastic and dielectric singularities. These were followed by semicontinuum Mott-Littleton techniques and the Kanzaki defect force techniques in application to charged and neutral defect species. However the importance of a correct assessment of the dielectric polarization and the anharmonicity of the forces in the evaluation of the enthalpies and volumes have been well documented. Numerical computations of the enthalpies are seen to be sensitive to the choice of potential parameters and polarization models to varying degrees. While the theoretical picture is relatively clear in the case of the simpler materials with a near-ideal pure disorder, materials with mixed type of point defect disorders call for a more challenging simulation of defect environments which among other things should take into account the strong inhomogeneities of defect fields. The paper gives an overview of the evolution covering the highlights of these developments.</span