小中大【回复】
我认为超过2完全是可能的，没有问题。
引用CCL上的一段讨论
why do you think that an oscillator strength f = 2.7 is unphysical? This is certainly a large value, but it is not necessarily unreasonable. With TD-PBE1PBE/6-31+G*, we obtained f = 2.2 for the first optically allowed electronic transition in the D2d conformation of diphenyldiacetylene, see Thulstrup et al., PCCP 13, 16168-16174 (2011).
According to Thomas-Reiche-Kuhn sum rule, the f-value for an electronic transition is not limited to magnitudes below or equal to unity, it may increase unity. As a matter of fact, it frequently does. For example, the experimental oscillator strength for the first transition in all-trans beta-carotene is equal to f = 2.7. This is the value obtained by integration over the absorption band in hexane with maximum at 22200 cm-1 and eps = 139400 (cuturl('http://omlc.ogi.edu/spectra/PhotochemCAD')), yielding f = 4.32E-9 * INT = 2.73. For the extremely strong band with maximum at 44800 cm-1 and eps = 1.1E6, integration yields f > 7.
