A summary of the parametric potential metliod is presented : the central potential introduced by Slater is expressed as an analytical function of some parameters, which can be optimalized according to several quality criteria. A spectroscopic criterion - where the r. m. s. deviation between theory and experiment is minimalized - was applied to rare gases Ne I through Rn I, and to the isoelectronic sequence Ne I to V XIV. Once relativistic corrections are introduced, as well as configuration mixing, r. m. s. ƊE are smaller than 500 cm-1, for computed spectra of c. a. 100,000 cm-1. As for the isoelectronic sequence, we were able to interchange names ascribed to levels 2 p5 3 d 1P1 and 2 p5 3 d 3D1. A variational criterion - minimalization of ground state first order energy - yields results very near those of Hartree-Fock, and is useful as a starting point for perturbation studies