Variational calculation for the ground state of lithium and the QED corrections for Li-like ions

High-precision variational calculations using multiple basis sets in Hylleraas coordinates are presented for the 1s²2s ²S state of lithium. The variational bound of -7.478 060 326(10) a.u. for the nonrelativistic energy is in good agreement with our revised experimental value of -7.47 806 034(20) a.u., thereby resolving a long-standing disrepancy. Two-electron calculations of the QED corrections are extended to three-electron systems and compared with other results. The comparison for Li-like ions up to U⁸⁹⁺ suggests a simple interpretation for the ``screening of the Lamb shift'' recently calculated by Cheng, Johnson, and Sapirstein [Phys. Rev. Lett. 66, 2960 (1991)].