A variational approach to the partition function of an interacting many body system Original Research Article

For the calculation of the partition function Z of small, isolated and interacting many body systems an improvement with respect to previous formulations is presented. By including inharmonic terms and employing a variational approach quantum effects can be treated even at very low temperatures. In order to test its accuracy the novel approach is applied to the exactly solvable Lipkin–Meshkov–Glick model (LMGM). For thermodynamic properties and level densities good agreement with the exact calculations is found.