The ground state energies of the two-electron ions from H— to Ne8+ are calculated for the simple wave function (1s1s′)+λ(2p)2 with optimized orbital exponents. The use of the difference between the calculated energy and the experimental energy as a function of the atomic number for accurate extrapolation is explored. The expectation values of the operators rn(n≥—2), δ(3)(r1), and δ(3)(r12) are compared with those obtained from more accurate wave functions.

The well-known perturbation expansion, £ ?tr w(Z)=Z 2 2 c-wz-S of the eigenvalues of the nonrelativistic Schrodinger equation for N electrons about a nucleus of charge Z, has been widely used in the past for the extrapolation and interpolation of atomic energies. The presence of many small effects not explicitly taken into account by the perturbation expansion analysis reduce such calculations to a process of empirical curve fitting of limited range and reliability. These small effects include relativistic effects, the mass polarization, and the Lamb terms; to a good approximation, these effect can also be expanded in a descending power series, but with a leading term containing Z 8 . On the basis of three plausible assumptions, theoretical approximations make it possible, in a semiempirical fashion, to remove a major portion of these small effects from the experimental data. In this way accurate values for e 2 (N) and good estimates for e s (N) have been obtained for 3^.N^ 10. These coefficients have been used to disclose inaccuracies and to fill gaps in the existing atomic energy data and to estimate electron affinities. GROUND STATE OF ISOELECTRON1CATOMIC SERIES 831

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Large-order perturbation theory has been applied, for the first time, to the Stark effect for H2"'", yielding the Rayleigh-Schrodinger ground-state eigenvalue (polarizability) series through twentieth order; previous expansions were limited to fourth order. The calculations were performed nonadiabatically (i.e., without invoking the Born-Oppenheimer approximation) by means of the perturbational-variational Rayleigh-Ritz formalism. The leading terms of the Rayleigh-Schrodinger polarizability series so obtained provide the most accurate values thus far determined for azz and PACS numbers: 32.60. + i, 02.30. + g, 31.20.Di

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