Modeling of Ribbon and Oblique Structures of Benzene-1,3,5-triyl-tribenzoic Acid
Andrius Ibenskas, E. E. Tornau
Abstract
We propose two models describing the self-assembly of intact and deprotonated benzene-1,3,5-triyl-tribenzoic acid (BTB) molecules into the oblique (O) and ribbon (R) phases. The models are also extended to describe the formation of the honeycomb (HON) structure. To determine the intermolecular interaction potentials for the R and O phases, we performed the DFT calculations for the clusters of neutral and charged BTB molecules. The obtained values were used as an input in the Monte Carlo (MC) simulations. The model and MC simulations for the R phase demonstrate how ionic interactions between singly deprotonated BTB molecules lead to the formation of ribbons separated by the interribbon gap, and how these ribbons pack into the ordered two-dimensional structure. The O phase is treated in our model as the structure that might be composed of both intact and singly deprotonated molecules, owing to the occurrence of this phase in polarization switching experiments for positive surface bias. The ground-state analysis and MC modeling for the O and HON structures with the DFT-calculated interaction parameters demonstrate that for intact molecules (deprotonation level (DPL) = 0) the energy of the HON structure is always lower than that of the O phase. With an increase of DPL, the difference between the energies of these two structures decreases: while for DPL = 0.5, the possibilities to obtain the HON or O phase are very similar, for DPL = 1 the O phase has a higher probability to exist in comparison to the HON phase.