Conventional gas surface interaction (GSI) models and molecular dynamics (MD) simulations have been compared with angular distributions and average translational energies for N2 scattered from highly oriented pyrolytic graphite (HOPG) measured by angle and velocity resolved molecular beam scattering experiments. The translational energy and angular distributions of the scattered N2 were obtained for incidence energies near 30 and 68 kJ mol–1, incidence angles of 30°, 45°, and 70°, and a surface temperature of 677 K. The trajectories of scattered nitrogen molecules were found to fall into three main categories, i.e., single collision, multiple collisions with escape, and multiple collisions without escape. While the conventional GSI models did not match the translational energy and angular distributions obtained from the experiments, the results obtained from MD simulations were found to be in good agreement. The MD simulations also showed that the number of surface layers used to model the HOPG surface and the carbon–nitrogen Lennard-Jones potential are important in improving the agreement between the simulations and the experiments.

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The effects of an external electric field on two ionic liquids (ILs) are investigated using molecular dynamics electrospray simulations of ethylammonium nitrate (EAN) and ethanolammonium nitrate (EOAN). In the absence of an external electric field, long alkyl chains were observed in EAN but not in EOAN. When the electric field was applied, the anions of both ILs formed a barrier along the applied field, but only in EAN did this barrier result in a static bilayer composed of two parallel layers of cations and anions. The primary hydrogen bonds (HBs) connecting the EAN cations and anions were formed between the ammonium and the nitrate groups. In contrast, they were formed between the ammonium as well as the hydroxyl groups and the nitrate groups in EOAN. The applied electric field was found effective in reducing the number of O-H⋯O type HBs but was less effective against the N-H⋯O type HBs. It was observed that the N-C-C backbone angles of EAN allowed for greater storage of the energy supplied by the electric field in the form of torsional degree of freedom compared to the N-C-C angles of EOAN. The combination of stronger HBs and higher energy storage in the N-C-C covalent angle in EAN results in a stronger resistance of ion emission from the bulk compared to EOAN.

Molecular dynamics (MD) electrospray simulations of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF_{4}) ion liquid were performed with the goal of evaluating the influence of long-range Coulomb models on ion emission characteristics. The direct Coulomb (DC), shifted force Coulomb sum (SFCS), and particle-particle particle-mesh (PPPM) long-range Coulomb models were considered in this work. The DC method with a sufficiently large cutoff radius was found to be the most accurate approach for modeling electrosprays, but, it is computationally expensive. The Coulomb potential energy modeled by the DC method in combination with the radial electric fields were found to be necessary to generate the Taylor cone. The differences observed between the SFCS and the DC in terms of predicting the total ion emission suggest that the former should not be used in MD electrospray simulations. Furthermore, the common assumption of domain periodicity was observed to be detrimental to the accuracy of the capillary-based electrospray simulations.