Anomalous heat conduction in polyethylene chains: Theory and molecular dynamics simulations

In 1955 Fermi, Pasta, and Ulam showed that a simple model for a nonlinear one-dimensional chain of particles can be nonergodic, which implied infinite thermal conductivity. A more recent investigation of a realistic model for an individual polyethylene chain suggests that this phenomenon can even persist in real polymer chains. The reason for the divergent behavior and its associated mechanism, however, remains unclear. This paper presents a general formulation for normal-mode vibrational contributions to thermal conductivity, which is then used to analyze molecular dynamics simulations of individual polyethylene chains. Our analysis shows that cross correlations for midfrequency longitudinal-acoustic phonons are responsible for the divergent thermal conductivity in our model.