The ground state of the $\alpha$ particle is calculated using a revised version of the Brillouin-Wigner perturbation method, with enhanced variational flexibility. The resulting energy eigenvalue, for the Paris potential, is -25.5 MeV. When Coulomb forces and possible errors are taken into account one establishes an upper bound on the eigenvalue of -24.1 MeV. The derived wave function contains a $D$ state admixture of only 5.36%.

• Received 18 November 1983

DOI:https://doi.org/10.1103/PhysRevC.29.1444