Abstract: The full-core plus correlation method(FCPC)is extended to calculate the energies and fine structures of 1s²4p states for the lithium-like systems with nuclear charge from Z=11 to 20.The transition energies(2s²S_1/2-4p²P_1/2,3/2) and dipole oscillator strengths are also calculated.The non-relativistic energies and wave functions are calculated by the Rayleigh-Ritz method.Relativistic and mass-polarization effects on the energies are included as the first-order perturbation corrections.The quantum-electrodynamics contributions to the transition energies are estimated by using the effective nuclear charge.Our results are in agreement with the experimental data available in the literature.

Key words: lithium-like ion, fine-structure, transition energy, oscillator strength