The contribution of two-particle-two-hole excitations to the Hartree-Fock energy in the ground state of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ favors an axially symmetric prolate shape over the nonaxial shape preferred on the basis of bare Hartree-Fock calculations. The second-order contribution, however, does not affect the prediction of Hartree-Fock calculations of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$.

• Received 30 September 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1936