In this paper, a numerically detailed thermodynamic investigation of nucleosomal core particles is presented. The nonlinear Poisson-Boltzmann equation governs the electrostatic properties of both the DNA and histone protein. Brownian dynamics is used as the leading method, in combination with the analysis of the electrical features of the nucleosome. At elevated temperature, the structure of the nucleosome is destabilized by the decrease in electrical interactions of DNA-histone complexes, which can be explained with the EDL theory. Two obvious unwrapping transitions can be found, occurring within the temperature ranges 43-52 and 65-80 degrees C. The first transition is characterized by the melting of DNA terminal domains, and the feature of the second transition is the massive unwrapping of the DNA middle domain. It can be concluded that the nucleosomal DNA consists of two distinct structures, where the DNA terminal domains are less tightly bound to the histone than the DNA middle domain.