Curvature maxima in two-state systems: A semi-classical study

In an interacting two (electronic-) state model of molecules with one (effective) nuclear degree of freedom the normalized mean square deviation of the curvature (NMSDC) shows a temperature-maximum. The maximum increases with decrease of the interaction strength, but undergoes a sharp transition to no maximum, when the interaction term vanishes. The NMSDC maximum serves as a geometric hallmark for the underlying potential. The analogous result found by Mazzoni and Casetti [L.N. Mazzoni, L. Casetti, Phys. Rev. Lett. 97 (2006) 218104] for folding proteins can be reproduced by this elementary interacting two state model.