金属对电磁场的响应包括自由和束缚电荷两部分的贡献，大学物理教学中通常分别用Drude 模型和Lorentz 模型描述，然而，以上模型所得的介电函数只在一段较窄的频率范围内能与实验数据吻合.因此，在实际科研工作中，当物理量与较宽频率范围内的电磁场响应有关时，原则上介电函数应当采用实验测量值而不能采用模型化的结果.本文以金属纳米球诱导的二能级系统的基态能级移动为例，分别展示采用模型化的介电函数和实验介电函数时，能级移动计算结果的差异.

The electromagnetic response of metal contains the contribution of the free charges and the bound charges，which are usually theoretically descripted by the Drude model and the Lorentz model in collage physics respectively. However，only in a certain frequency range that the prediction from both models agrees with the experimental values. In practical scientific research，one should make use of the experimental values of the dielectric constant instead of the results from the Drude model or the Lorentz model when the physical quantity is related to the response over a wide frequency range in principal. In this work，the energy level shift of a ground two-level system around a metal nanosphere is numerically demonstrated with the electric permittivity of metal from the Drude model and the experimental values. Significant difference is observed，which implies the importance of the correct usage of the electric permittivity of metal.