Calculation of resonance states of positronic lithium atom

Feshbach resonance states of positronic lithium atom are precisely calculated with a Gaussian expansion method. By adopting a Lorentzian formula for density of state, resonance energies and widths are systematically determined from series of energy levels calculated by a real scaling method. We identify Feshbach resonance states between Li (2p) + e+ and Li (4s) + e+ thresholds and the results are in good agreement with previous works with the real scaling method and complex scaling method. Our results of a dipole series of resonances supported by ion-dipole interaction of Li+-Ps (n = 2), whose existence has been pointed out by previous works, show a good agreement with the latest calculation with a complex scaling calculation. We point out that an accuracy of the model potential for the electron and positron from the atomic ion is significant for the positronic atom formation process