Phyllosilicates, including the clay minerals talc, pyrophyllite and montmorillonite, are associated with numerous environmental, agricultural and industrial processes. Due to the lack of well-crystallized materials, experimental determinations of the crystal structure and mineral behavior for most clay minerals are difficult to obtain. Molecular simulations, however, provide an opportunity to evaluate the detailed structure and dynamics for idealized models of these complex clay phases, usually as a supplement to the limited x-ray diffraction and vibrational spectroscopy data.

In this work, the structural and vibrational properties of charged and uncharged phyllosilicates are investigated with ab initio and classical molecular dynamics simulations and compared with IR and Raman spectroscopic experiments. The quantum mechanical simulations are based on density functional theory (DFT), which is sufficiently accurate to predict the structural and vibrational properties of clay minerals. However, to understand the nature of adsorption, diffusion, and other complex processes in clay minerals, simulation of these systems in a full quantum mechanical manner becomes infeasible due to the computational burden. The classical molecular dynamics (MD) simulation using an accurate force field (CLAYFF) is a viable alternative, where it has been shown to faithfully reproduce the crystal structures with relatively simple analytical functions that include primarily non-bonded interactions.

Critical to the understanding of adsorption properties in charged and uncharged clays is the disposition of the hydroxyl group in the octahedral sheets. Signature spectroscopic peaks that are characteristic of the hydroxyl group vibrations and bends are easily identified experimentally. With the assistance of molecular simulation, the relationship between hydroxyl group vibrational modes and the molecular-scale structure is explored. In particular, the orientation of the hydroxyl group is closely monitored to understand the effects of the dioctahedral vacancy and counterbalancing cations on the clay behavior. Overall, the structures obtained from ab initio and classical molecular dynamics simulations provide a detailed understanding of the important interactions that influence the adsorption properties of clay minerals.