Transition interface sampling (TIS) was introduced to improve the efficiency of the rate calculation, associated with TPS. In TIS, configuration space is sectioned into non-intersecting interfaces based on a CV (usually indicated with 𝜆 in the TPS/TIS literature). The order parameter lambda should enable a mutually exclusive partitioning of the configuration space between a reactant basin, where 𝜆 < 𝜆 𝐴 = 𝜆 0 and a product basin where 𝜆 > 𝜆 𝐵 = 𝜆 𝑛 . The reaction rate constant 𝑘 𝐴𝐵 is then obtained as :