Computation of the Dissociation Temperature of TBAB Semiclathrate in an Aqueous Solution Using Molecular Simulations

Quaternary ammonium salts such as tetra-n-butyl ammonium bromide (TBAB) are known to form semiclathrate hydrates. Since they form at much milder conditions compared to gas hydrates, they have evoked much interest in development of new technologies for gas storage and gas separations. In this work, we present a method to compute the phase equilibrium of TBAB semiclathrate. The TBAB molecule is modeled using OPLS-AA and GAFF force fields and the results from simulations are compared with experimental data to determine the ability of the force fields to accurately predict the semiclathrate phase equilibria. It was observed that the OPLS-AA force field outperforms the GAFF force field in predicting the experimental phase equilibrium data.

Modeling of effective interactions between ligand coated nanoparticles through symmetry functions

Ligand coated nanoparticles are complex objects consisting of a metallic or semiconductor core with organic ligands grafted on their surface. These organic ligands provide stability to a nanoparticle suspension. In solutions, the effective interactions between such nanoparticles are mediated through a complex interplay of interactions between the nanoparticle cores, the surrounding ligands, and the solvent molecules. While it is possible to compute these interactions using fully atomistic molecular simulations, such computations are too expensive for studying self-assembly of a large number of nanoparticles. The problem can be made tractable by removing the degrees of freedom associated with the ligand chains and solvent molecules and using the potentials of mean force (PMF) between nanoparticles. In general, the functional dependence of the PMF on the inter-particle distance is unknown and can be quite complex. In this article, we present a method to model the two-body and three-body PMF between ligand coated nanoparticles through a linear combination of symmetry functions. The method is quite general and can be extended to model interactions between different types of macromolecules.