  In single-molecule force spectroscopy experiments, the dependence of the mean
unfolding force on the loading rate is used for obtaining information about the
energetic and dynamic properties of the system under study. However, it is
crucial to understand that different dynamic force spectroscopy (DFS) models
are applicable in different regimes, and that different definitions of the
unfolding force might be used in those models. Here, for the first time, we
discuss three definitions of the unfolding force. We carried out Brownian
dynamics simulations in order to demonstrate the difference between these
definitions and compare DFS models. Importantly, we derive the dependence of
the mean unfolding force for the whole range of the loading rates by unifying
three previously reported DFS models. Among the currently available models,
this unified model shows the best agreement with the simulated data.
