Shape ofMg24at zero and finite temperature

Hartree-Fock-Rothaan calculations with realistic effective interactions in the sd shell consistently yield an ellipsoidal ground-state deformation for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. The predictions of the present mean-field calculations are supported by experiment and exact shell-model calculations. For a deformed ground state with ellipsoidal symmetry two shape transformations are observed in the finite-temperature Hartree-Fock approximation as the temperature is increased, firstly from ellipsoidal to axially symmetric and finally to a spherical shape.