Canonical Entropy of charged black hole
  Recently, Hawking radiation of the black hole has been studied by using the tunnel effect method. It is found that the radiation spectrum of the black hole is not a strictly pure thermal spectrum. How does the departure from pure thermal spectrum affect the entropy? This is a very interesting problem. In this paper, we calculate the partition function through energy spectrum obtained by using the tunnel effect. From the relation between the partition function and canonical entropy, we can derive the entropy of charged black hole. In our calculation, we consider not only the correction to the black hole entropy due to fluctuation of energy, but also the effect of the change in the black hole charges on entropy. There is not any assumption. This makes our result more reliable. 
Zhao Ren, Li Huai-Fan, Zhang Sheng-Li