Thermal conductivity in a one-dimensional Lennard-Jones chain by molecular dynamics

Cluster sizes in a classical Lennard-Jones chain

The definitions of breaks and clusters in a one-dimensional chain in equilibrium are discussed. Analytical expressions are obtained for the expected cluster length, 〈K〉, as a function of temperature and pressure in a one-dimensional Lennard-Jones chain. These expressions are compared with results from molecular dynamics simulations. It is found that 〈K〉 increases exponentially with β=1/k_{B}T and with pressure, P in agreement with previous results in the literature. A method is illustrated for using 〈K〉(β,P) to generate a "phase diagram" for the Lennard-Jones chain. Some implications for the study of heat transport in Lennard-Jones chains are discussed.

Nonequilibrium molecular dynamics simulations of heat flow in one-dimensional lattices

We study the use of the Evans nonequilibrium molecular dynamics (NEMD) heat flow algorithm for the computation of the heat conductivity in one-dimensional lattices. For the well-known Fermi-Pasta-Ulam model, it is shown that when the heat field strength is greater than a certain critical value (which depends on the system size) solitons can be generated in molecular dynamics simulations starting from random initial conditions. Such solitons are stable and travel with supersonic speeds. For smaller heat fields, no solitons are generated in the molecular dynamics simulations; the heat conductivity obtained via the NEMD algorithm increases monotonically with the size of the system.