Intermolecular potentials for simulations of collisions of SiNCS ~+ and (CH _3) _2SiNCS ~+ ions with fluorinated self-assembled monolayers

摘要

Analytical potential energy functions were developed for interactions of SiNCS ~+ and (CH _3) _2SiNCS ~+ ions with perfluorinated self-assembled monolayer (F-SAM) surfaces. Two model compounds were used to represent an F-SAM: CF _4 and nine chains of perfluorobutane forming a miniSAM structure. Density functional theory plus dispersion (DFT-D) calculations were carried out to compute intermolecular potential energy curves (IPECs) for these systems. The applied DFT-D method (specifically, B97-D) was successfully tested against high-level wavefunction calculations performed on the smallest system investigated. The IPECs calculated at the B97-D level were fitted to analytical potentials of the Buckingham type. The calculations show that the parameters obtained from the fits involving CF _4 are transferable to the miniSAM system, provided the fittings are conducted with caution, thus corroborating that CF _4 is a good model for parameterizing intermolecular potentials for interactions of gases with F-SAM surfaces.