CORRELATED FINITE-TEMPERATURE MEAN-FIELD APPROXIMATIONS

A correlated finite temperature mean field approximation is compared w ith the exact canonical, the conventional finite temperature Hartree-F ock and canonical finite temperature Hartree-Fock approximations in Ne -20. The thermal behavior obtained in the correlated approach with a r ealistic effective interaction differs substantially from that given b y mean field calculations. There are no sharp transitions and the syst em remains deformed at temperatures above the critical temperature of the deformed-to-spherical shape transition observed iii the mean field calculations in agreement with the exact canonical results. This sugg ests rather strongly that using collective deformation parameters obta ined from finite temperature mean field calculations as order paramete rs to describe the universal features of the nuclear shape transition may be misleading.