Determination of accurate quantum defects and wavefunctions for alkali Rydberg states with high principal quantum numbers

Quantum defects and the corresponding wavefunctions are determined for lithium, sodium, and potassium using a new method that searches for the poles of the Schwinger (1947) T matrix along the negative real energy axis. A Coulomb Green's function is used to factor out the effect of the long-range potential. Model potentials are employed to include the effects of core polarization and correlation. Quantum defects accurate to 1 percent are obtained with small basis sets and small grids. The method has been tested and found to be numerically stable for states with principal quantum number n as high as 80.