Improved Hylleraas calculations for ground state energies of lithium ISO–electronic sequence

The 2S ground state of lithium iso–electronic sequence is calculated by the use of Hylleraas‐type wave functions. A 92 term one‐spin wave function was used for lithium atom calculations. The energy obtained was −7.478031 a.u. as compared with the previous best value of −7.478025 a.u. calculated by Larsson. In addition, improved energies for Z = 4 to 8 were calculated by the use of 60 term wave functions. This work thus provides the lowest ab initio ground state energies for lithium sequence to date.