Reliable extraction of energy landscape properties from critical force distributions

The structural dynamics of biopolymers such as proteins are described in the context of their conformational energy landscapes. In pulling experiments using optical tweezers, features of the energy landscapes are extracted from the probability distribution of the critical force at which the polymer unfolds, and typically the analysis is based on rate equations having Bell-Evans form. We argue that this analysis is inadequate and leads to unreliable landscape parameters in many common situations. We propose a modified closed-form expression for the distribution of critical forces that works better for parameter extraction and is valid even up to fast pulling rates. We present results based on simulated data that confirm the utility of our new formula.