Conformational dynamics and finite-temperature infrared spectra of the water octamer adsorbed on coronene

We present in this work a detailed study of all-atoms conformational dynamics and finite temperature infrared (IR) spectra of the water octamer (H2O)8 adsorbed on coronene (C24H12), a compact Polycyclic Aromatic Hydrocarbon (PAH). The potential energy surface is calculated on-the-fly within the self-consistent-charge density-functional based tight-binding (SCC–DFTB) approach, with modifications insuring the correct description of water–water and water–PAH interactions. On-the-fly Born–Oppenheimer molecular dynamics simulations are performed in the temperature T range 10–300 K starting from the most stable cubic conformer of (H2O)8 adsorbed on C24H12. As T increases, diffusion of (H2O)8 starts, followed by isomerisation processes and “melting” of (H2O)8 for T in the range 150–200 K. These dynamical processes are quantified through the temperature evolution of chosen indicators. We show that the adsorption of (H2O)8 on C24H12 leads to lower isomerisation temperatures than for the bare cluster, in line with an increase of the density of isomers. A comparative analysis of the low-T (harmonic) spectra of bare and adsorbed (H2O)8 is provided. Finally, the evolution of the spectra as a function of T, illustrating the conformational dynamics, is discussed.