thank you for your reply, it is about the miscroscopic model of nuclear physics, the frictional cooling method is a variational method, i cannot understand it. the paper: Phys. Rev. C 52, 628–646 (1995) Structure of Li and Be isotopes studied with antisymmetrized molecular dynamicsIs "varional" a word, or did you make a typo? Please give references to the papers you're talking about. Is this a nuclear physics question, or a nuclear engineering question?