  Ring polymer molecular dynamics (RPMD) is an accurate method for calculating
thermal chemical reaction rates. It has recently been discovered that
low-temperature calculations are strongly affected by the simulation
parameters. Here, for the thermally activated reaction DH + H -> D + H2, we
calculate the RPMD rate constants at T = 50, 100, and 300 K and demonstrate
that for T >= 100 K the standard input parameters yield accurate results, but
at low temperatures (e.g., 50 K) one must increase the asymptotic distance and
force constant, and decrease the umbrella integration step.

Chemical Physics