where µ i is the electron mobility in the i-th structure and ∆E i is its lattice energy difference with respect to the predicted global minimum for that molecule. β = 2.70 kJ/mol is a decay constant fitted to the probability of observing a pair of polymorphs with an energy difference of ∆E i . This quantity provides a measure of the collective likelihood that a given molecule will crystallize into a structure with a large carrier mobility.