(508a) Development of Force Fields to Model Upcoming 2D Materials in Mechanical and Interfacial Applications

Authors: 
Govind Rajan, A., Massachusetts Institute of Technology
Sresht, V., Massachusetts Institute of Technology
Pádua, A. A. H., Institut de Chimie de Clermont-Ferrand, Université Blaise Pascal and CNRS
Strano, M., Massachusetts Institute of Technology
Blankschtein, D., Massachusetts Institute of Technology
The controlled synthesis of two-dimensional (2D) materials, such as molybdenum disulfide (MoS2) and hexagonal boron nitride (hBN), using liquid-phase exfoliation, as well as several of their proposed applications, such as desalination membranes, involve liquids coming into intimate contact with 2D material surfaces. Molecular dynamics (MD) simulations offer a robust methodology to investigate not only the mechanical properties of nanomaterials, but also nanomaterial/liquid interactions involving weak van der Waals forces. However, there were no MD force fields for MoS2 and hBN which could correctly describe the cohesive interactions between layers of these 2D materials, as well as the adhesive interactions of these materials with liquids such as water. In this talk, I will describe the development of a set of force-field parameters, using lattice dynamics calculations, that reproduce the properties of bulk 2-H molybdenite, with special attention to the distinction between the covalent, intra-layer terms, and the non-covalent, inter-layer Coulombic and van der Waals interactions. The resulting model is compatible with MD force fields for organic compounds, and can correctly describe the interactions of MoS2 with liquids, yielding excellent agreement with experimental contact angles for water and diiodomethane. Further, for hBN, we utilized density-functional-theory-based ab initio molecular dynamics (MD) simulations and lattice dynamics calculations to develop a classical force field. The new force field predicts the crystal structure, elastic constants, and phonon dispersion relation of hBN with good accuracy, and exhibits remarkable agreement with the interlayer binding energy predicted by random-phase approximation calculations. I will also demonstrate the importance of including Coulombic interactions, while excluding 1-4 intrasheet interactions, to obtain the correct phonon dispersion relation. Combining the force field for hBN with the accurate TIP4P/Ice water model yields excellent agreement with interaction energies predicted by quantum Monte Carlo calculations. Our force field should enable an accurate description of MoS2 and hBN interfaces in classical MD simulations aimed at mechanical and interfacial applications, thereby paving the way for the simulation-aided design in applications including membranes, microfluidic devices, and sensors.