Modeling lithium-ion solid-state electrolytes with a pinball model

Abstract

We introduce a simple and efficient model to describe the potential energy surface of lithium diffusing in a solid-state ionic conductor. First, we assume that the Li atoms are fully ionized and we neglect the weak dependence of the electronic valence charge density on the instantaneous position of the Li ions. Second, we freeze the atoms of the host lattice in their equilibrium positions; consequently, also the valence charge density is frozen. We thus obtain a computational setup (the "pinball model") for which extremely inexpensive molecular dynamics simulation can be performed. To assess the accuracy of the model, we contrast it with full first-principles molecular dynamics simulations performed either with a free or frozen host lattice; in this latter case, the charge density still readjusts itself self-consistently to the actual positions of the diffusing Li ions. We show that the pinball model is able to reproduce accurately the static and dynamic properties of the diffusing Li ions -including forces, power spectra, and diffusion coefficients -when compared to the selfconsistent frozen-host lattice simulations. The frozen-lattice approximation itself is often accurate enough, and certainly a good proxy in most materials. These observations unlock efficient ways to simulating the diffusion of lithium in the solid state, and provide additional physical insight into the respective roles of charge-density rearrangements or lattice vibrations in affecting lithium diffusion. arXiv:1805.10263v1 [cond-mat.mtrl-sci]

High-throughput computational screening for solid-state Li-ion conductors

“…5.6, with a minimum distance criterion d i nner = 8 Å between opposite faces. The Hamiltonian of the pinball model [91] is:…”

“…Calculating the diffusion of Li ions in a screening scenario accurately, with molecular dynamics, calls for a different approach, that combines the computational efficiency of force fields with the generality and accuracy of density-functional theory. We recently proposed the pinball model [91] as an accurate framework for the dynamics of Li ions in the solid state. Details and derivation are in the original paper, but we iterate here the key assumptions behind the model.…”

“…The diffusion coefficient from FPMD is not well reproduced by the pinball model, which can have several causes. First, the local pinball could be inaccurate, compared to the non-local pinball[91].…”

Unsupervised landmark analysis for jump detection in molecular dynamics simulations

“…The necessary compromise between the transferability of first-principles potential energy surfaces and the computational efficiency of force * These two authors contributed equally to this work. fields has also motivated the development of novel hybrid quantum/classical approaches [25] to model diffusion. The estimate of transport coefficients from the Green-Kubo or Einstein relations using molecular dynamics can be done in a straightforward yet expensive way, though improved methods for obtaining accurate estimates from short trajectories are being developed [26].…”

Topological quantization and gauge invariance of charge transport in liquid insulators

“…We conclude by expressing our confidence that the results presented in this paper will have a strong impact on both computer simulations and fundamental research. On the more practical side, our findings will allow a considerable simplification of the quantum numerical modelling of ionic conduction in complex systems and materials such as, e.g., ionic liquids [26] or solid-state electrolytes [27], avoiding, in many cases, the cumbersome and time-consuming computation of Born effective charges. On a more fundamental side, our work provides a solid topological foundation and generalisation to liquids of the definition of ionic oxidation states already available for solids [7].…”