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Physical Chemistry Seminar
September 8, 2017 @ 4:10 pm - 5:00 pm
Dr. Maxime Pouveau, Post-doc for Professor Aurora Clark, will present a seminar in Fulmer 150 at 4:10pm.
Title: Structure and dynamics of hydrated mineral edge surfaces: molecular dynamics simulations based on the density functional theory (DFT) and on an improved empirical model
Abstract: Molecular scale understanding of the structure and properties of aqueous interfaces with clays, metal (oxy-)hydroxides, layered double hydroxides, and other inorganic phases is strongly affected by significant degrees of structural and compositional disorder of the interfaces. An empirical model (ClayFF) was originally developed for classical molecular simulations of such systems. However, despite its success, multiple limitations have also become evident with its use. One of the most important limitations is the difficulty to accurately model the edges of finite size nanoparticles or pores rather than infinitely layered periodic structures. A simple and efficient approach to solve this problem uses metal‑O‑H (M‑O‑H) angle bending terms to better describe the structure and dynamics of hydroxyl groups at mineral surfaces, particularly edge surfaces. Density functional theory (DFT, PW91-D3/DZVP) was used to determine optimal values of Al‑O‑H, Mg‑O‑H and Si-O-H bending parameters.
Molecular dynamics simulations were performed both at the DFT and at the classical level for model surfaces of minerals in contact with water: the basal and edge surfaces of gibbsite, Al(OH)3, brucite, Mg(OH)2, and the edge surface of kaolinite, Al2Si2O5(OH)4. The orientation of the hydroxyl groups, the interfacial hydrogen bonding statistics, and the vibrational spectra were obtained from the simulations at the DFT level and at the classical level. The addition of the new bending term leads to a more accurate representation of the orientation of hydroxyl groups and of its librational dynamics at the basal and edge surfaces. The previously observed excessive desorption of OH2 groups from the particle edges within the original force field is also constrained by the new modification.