Excitation Energies of 1s2ns (6 ⩽ n ⩽ 9) States for Lithium-Like Systems from Z =11 to 20

Abstract

The non-relativistic energies of 1s2ns (6 ⩽ n ⩽ 9)states for the lithium-like systems from Z = 11 to 20 arecalculated by using a full-core-plus-correlation (FCPC) method. Therelativistic and mass-polarization effects on the energy are calculatedby the first-order perturbation corrections. The correction from thequantum-electrodynamics effect is also included using effective nuclearcharge. Based on these results and the quantum defect theory, thequantum defects of 1s2ns series for these ions, as afunction of energy, are determined. The comparisons between theionization potentials for 1s2ns states (6 ⩽ n ⩽ 9)obtained by the FCPC method and the semi-empirical method are carriedout. The results show that their agreement is very well and theenergies of all discrete states (n ⩾ 10) below the ionizationthreshold of this series for the ions can be predicted by using theirquantum defects.