Electron - capture decay rate of 7 Be @ C 60 by first - principles calculations based on density functional theory

Carrying out a first-principles calculation assuming linear relationship between the electron density at Be nucleus and the electron-capture EC decay rate, we explained why Be@C60 shows higher EC decay rate than Be crystal, which was originally found experimentally by Ohtsuki et al. Phys. Rev. Lett. 93, 112501 2004 . From the results of the calculation, we found that there are inequivalent four stable i.e., lower energy Be sites inside C60 and that center of C60 C_C60 is the most favorable site. For C_C60, the electron density at the Be nucleus is the highest. It is also much higher than that at the Be nucleus in a Be crystal. Also, we estimated the expected electron density at the Be nucleus at room temperature by taking statistical average of the electron densities at the four Be nucleus sites using the Boltzmann distribution. The results of the calculation show fairly good agreement with the experimental results. In this paper, we focus on the detail of calculation, which was not fully demonstrated in the paper by Ohtsuki.