Dropping a Droplet of Cysteine Molecules on a Rutile (110) Interface: Reactive versus Nonreactive Classical Molecular Dynamics Simulations

Two different types of classical molecular dynamics approaches, based on reactive and nonreactive force-field parametrizations, are used to investigate the adsorption process of a nanodroplet of cysteine molecules onto a perfect and a defective rutile (110) surface in the gas phase. Three molecular samples made of different cysteine species, namely, one neutral and two zwitterionic models, are tested in order to check how much the starting configurations can bias the description of the deposition onto the surface and if the initial composition of the droplet can influence the final mixture and adsorption arrangements. The present comparison between the two classical computational strategies is useful to identify and suggest the most appropriate approach to depict the behavior of hybrid materials, which cannot be treated at the quantum dynamical level because of the prohibitive computational cost. The complex interaction mechanisms between the molecules of the isolated droplet far from the slab and when it is spread on the inorganic interface are represented reliably and effectively by the reactive dynamics, which is revealed to be a powerful and more appropriate methodology, in comparison with standard molecular dynamics, to disclose all the aspects connected with the process of adsorption. Indeed, differently from the usual nonreactive molecular dynamics, simulations based on reactive force fields do not require any arbitrary assumption on the nature of the adsorbed units and include chemical reactivity. This is often fundamental to identify the most relevant biomolecular species interacting with the inorganic supports and the proton exchange mechanisms acting at the interface.