  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.
