Intermolecular potentials for simulations of collisions of SiNCS+ and (CH3)2SiNCS+ ions with fluorinated self-assembled monolayers

Analytical potential energy functions were developed for interactions of SiNCS+ and (CH3)2SiNCS+ ions with perfluorinated self-assembled monolayer (F-SAM) surfaces. Two model compounds were used to represent an F-SAM: CF4 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 CF4 are transferable to the miniSAM system, provided the fittings are conducted with caution, thus corroborating that CF4 is a good model for parameterizing intermolecular potentials for interactions of gases with F-SAM surfaces