Ergodicity and dynamical properties of constant-temperature molecular dynamics

The assumption of ergodicity in Nosé’s original formulation of the constant-temperature molecular dynamics is tested for a Lennard-Jones-potential system. With the performance of very long simulations, it is shown that the extended system of a Lennard-Jones-potential system is ergodic for all values of thermostat parameters tested. It is also shown, however, that the rate of convergence to the canonical ensemble strongly depends on the value of thermostat effective mass Q. The dynamical properties of the extended system are also studied using the velocity autocorrelation function and the power spectral density. From the analysis of the simulations, it is found that the dynamical properties are not correctly represented for arbitrary values of thermostat parameters. A prescription and a set of quantitative criteria are introduced to generate physically meaningful dynamics. Thus the results of this work show that with a special choice of thermostat parameters it is possible to obtain both the correct canonical ensemble and physically meaningful dynamical behavior of the physical system.