where l 0 is the vibrational amplitude for the ground vibrational state (see Equation ), which can also be defined as l 0 = l quant (T = 0). For each given temperature, the classical vibrational amplitude does not exceed the quantum one (l class ≤ l quant ). However, it is possible to find the specific temperature at which the classical ensemble shows the same PDF as in the quantum case at T = 0. From the equation l class = l 0 , we obtain