Performance of Particle Swarm Optimization in Predicting the Orientation of π-Conjugated Molecules Inside Carbon...

Particle swarm optimization (PSO) was employed to obtain the global minimum of host-guest structures consisting of a triiodobenzene molecule (BzI₃) inside an armchair (m,m) nanotube (BzI₃@(m,m)), whose host-guest interactions are approximated by Lennard-Jones (LJ) potentials. The host-guest structures obtained using the PSO-LJ method were then compared with those obtained through dispersion-corrected density functional theory (DFT) calculations to evaluate the performance of the PSO-LJ approach in predicting the guest orientation inside a tube. When the inner space of the host tube is limited for guest encapsulation, the PSO-LJ method can reproduce the DFT results of BzI₃@(m,m) in terms of the guest orientation. Conversely, in nanotubes with a sufficiently large space to allow a guest to freely move, corresponding to weak tube confinement, the PSO-LJ method yields guest orientations that are different from those obtained through DFT calculations; however, both methods obtain energetically close guest orientations. Accordingly, PSO-LJ method-assisted DFT calculations can quickly provide energetically stable guest orientations in BzI₃@(m,m) in weak tube confinement, which can be ignored in DFT calculations, where a single initial geometry is typically used.