title: Normal versus anomalous self-diffusion in two-dimensional fluids: memory function approach and generalized asymptotic Einstein relation.
abstract: Based on the generalized Langevin equation for the momentum of a Brownian particle a generalized asymptotic Einstein relation is derived. It agrees with the well-known Einstein relation in the case of normal diffusion but continues to hold for sub- and super-diffusive spreading of the Brownian particle's mean square displacement. The generalized asymptotic Einstein relation is used to analyze data obtained from molecular dynamics simulations of a two-dimensional soft disk fluid. We mainly concentrated on medium densities for which we found super-diffusive behavior of a tagged fluid particle. At higher densities a range of normal diffusion can be identified. The motion presumably changes to sub-diffusion for even higher densities.
authors.affiliation: Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.
authors.forename: Hyun Kyung
authors.initials: HK
authors.lastname: Shin
authors.affiliation: Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.
authors.forename: Bongsik
authors.initials: B
authors.lastname: Choi
authors.affiliation: Universität Augsburg, Institut für Physik, D-86135 Augsburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Talkner
authors.affiliation: Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.
authors.forename: Eok Kyun
authors.initials: EK
authors.lastname: Lee