Emergence of Undulations and Determination of Materials Properties in Large-Scale Molecular Dynamics Simulation of Layered Double Hydroxides

Abstract

Layered double hydroxides (LDHs) have generated a large amount of interest in recent years because of their ability to intercalate a multitude of anionic species. Atomistic simulation techniques such as molecular dynamics have provided considerable insight into the behavior of these materials. The advent of supercomputing grids allows us to explore larger-scale models with considerable ease. Here, we present our findings from large-scale molecular dynamics simulations of Mg2Al-LDHs intercalated with chloride ions. The largest studied system size consists of one million atoms with lateral dimensions of 588 Å × 678 Å. The system exhibits emergent properties, which are suppressed in smaller-scale simulations. Undulatory modes are caused by the collective thermal motion of atoms in the LDH layers. At length scales larger than 20.7 Å, these thermal undulations cause the LDH sheets to interact and the oscillations are damped. The thermal undulations provide information about the materials properties of the system. In this way, we obtain values for the bending modulus of 8.3 ± 0.4 × 10-19 J with in-plane Young's moduli of 63.4 ± 0.5 GPa for a hydrated system and 139 ± 1 GPa for the LDH sheets alone.