Solvation of fullerene and fulleride ion in liquid ammonia: structure and dynamics of the solvation shells

Molecular dynamics simulations have been performed to investigate the solvation characteristics of neutral fullerene (C(60)) and charged fulleride anion (C(60)(5-)) in liquid ammonia. Potassium ions are present as counterions in the system containing fulleride ion. In addition to solvation characteristics, dynamical properties of solvation shells are also found out for both the neutral and anionic solutes. Our results reveal the presence of a rather large solvation shell of ammonia molecules around the C(60)(5-) ion. It is found that the ammonia molecules are more closely packed in the first solvation shell of C(60)(5-) than that of C(60). The distributions of ammonia molecules in the solvation shells of C(60) and C(60)(5-) solutes together with hydrogen bonding characteristics of the solvent in different solvation shells are investigated. It is found that the solvation of the small counterions (K(+)) in liquid ammonia is affected very little by the presence of the large C(60)(5-) anion. Regarding the dynamics of ammonia in solvation shells, it is found that the residence, translational and rotational dynamics of ammonia molecules differ significantly between the solvation shells of the neutral and charged fullerene solutes, especially in the first solvation shells. The average lifetimes of ammonia-ammonia hydrogen bonds are calculated from both continuous and intermittent hydrogen bond correlation functions. The calculations of binding energies reveal that the hydrogen bonds are weaker, hence short lived in the solvation shell of C(60)(5-) compared to those in the solvation shell of neutral C(60) and also in bulk liquid ammonia.