Ionization potential for ground states of berylliumlike systems

Abstract

The 1${\mathit{s}}^{2}$2${\mathit{s}}^{2}$ ground-state energies of berylliumlike systems are calculated with a full-core plus correlation method. A partial saturation of a basis-function method is used to extrapolate a better nonrelativistic energy. The 1${\mathit{s}}^{2}$2${\mathit{s}}^{2}$ ionization potentials are calculated by including the relativistic corrections, mass polarization, and QED effects. These results are compared with the existing theoretical and experimental data in the literature. The predicted Be i, C iii, N iv, and O v ionization potentials are within the quoted experimental error. Our result for F vi, 1 267 606.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, supports the recent experiment of Engstr\"om [Phys. Scr. 31, 379 (1985)], 1 267 606(2) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, over the datum in the existing data tables. The predicted specific mass polarization contribution to the ionization potential for Be i, 0.006 88 a.u., agrees with the 0.006 74(100) a.u. from the experiment of Wen et al. [Phys. Rev. A 37, 4207 (1988)]. The calculated relativistic correction to the double ionization of Be i, -0.000 135 0 a.u., also agrees with the recent result, -0.000 135 a.u., of Lindroth et al [Phys. Rev. A 45, 1493 (1992)]. Using the calculated results of Z=4--10, 15, and 20, we extrapolated the results for other Z systems up to Z=25 for which the ionization potentials are not explicitly computed.