  Infrequent Metadynamics is a popular method to obtain the rate of long
timescale processes from accelerated simulations. The inference procedure is
based on rescaling the first-passage times of Metadynamics trajectories using a
bias-dependent acceleration factor. While useful in many cases, it is limited
to Poisson kinetics, and a reliable estimation of the unbiased rate requires
slow bias deposition and prior knowledge of efficient collective variables.
Here, we propose an improved inference scheme, which is based on two key
observations: 1) The time-independent rate of Poisson processes can be
estimated using short trajectories only. 2) Short trajectories experience
minimal bias, and their rescaled first-passage times follow the unbiased
distribution even for relatively high deposition rates and suboptimal
collective variables. Therefore, by limiting the inference procedure to short
timescales, we obtain an improved tradeoff between speedup and accuracy at no
additional computational cost, especially when employing suboptimal collective
variables. We demonstrate the improved inference scheme for a model system and
two molecular systems.
