Time convergence

Here, a short demonstration on how time-correlation typically converges with total simulation time is provided for FCC Al at 300 K. To get a converged correlation function, e.g., in order to extract a phonon lifetime, one requires a simulation that is on the order of 100 to 1000 times longer than the lifetime itself. Rather than running a single long MD simulation, one can also run many shorter simulations and average their correlation functions.

In the figure below, the decay time of the correlation function is about 1 to 2 ps. The \(C_L(q, t)\) is pretty well-converged after 200 ps and very well converged after 2000 ps.

Current correlation \(C_L(q, t)\) for simulations of varying lengths.