4He adsorption on a single C40 molecule: Path integral Monte Carlo study

Abstract

Path-integral Monte Carlo calculations are performed to study the adsorption of 4He atoms on two different isomers of C40: one with the D2 symmetry and the other with the D5d symmetry. Here, we employ the 4He-C40 interaction described by the sum of 4He-C interatomic pair potentials, which allows us to examine the 4He corrugations on the fullerene molecular surfaces. We first observe the layer-by-layer growth of 4He on both C40 isomers, where the first layers are located at a distance of ~ 5.7 A from the molecular centers. From the investigation of the angular 4He density profiles, we find that the 4He layers display different quantum states depending on the number of 4He adatoms N. Between N = 22 and N = 40, the first 4He layer on the D2 isomer shows several different commensurate structures whereas the corresponding 4He layer on D5d undergoes a commensurate-to-incommensurate solid transition like the first 4He layer on graphite. As N increases, the superfluid responses of the first 4He layers on both isomers exhibit reentrant behavior with superfluidity being completely quenched at structurally-ordered states. In addition, the superfluid fraction of the first 4He layer is found to be about three times as large on D2 as on D5d for the same number of 4He atoms. The different structural and superfluid properties of 4He adatoms depending on the isomeric type could provide an experimental way of selecting a specific C40 isomer.