A calculation of the photoionization cross sections is presented for alkali-metal atoms such as Li and Na in plasma environments. The computational scheme is based on the complex coordinate rotation method. A model potential formalism has been used to simplify the computational complexity of the problems of making quantitative predictions of properties and interactions of many electron systems in Debye plasmas. The plasma environment is found to appreciably influence the photoionization cross sections. In this regard the photoionization cross sections of isolated atoms are also discussed that is found to be in good agreement with the previous theoretical results. It is observed that the strong plasma screening effect remarkably alters the photoionization cross sections near the ionization threshold. The Cooper minimum in the photoionization cross sections of Na shifts toward the higher energy as the plasma screening effect increases. For Li, the Cooper minimum is uncovered in strong plasma environments. This is the first time such structures have been determined.

We present the complex absorbing potential (CAP) method to investigate the Stark effect in hydrogen and lithium. The numerical technique as applied to calculations of Stark shifts and widths yields an appealing, simple and powerful tool for the computation of resonance parameters of the scattering processes. The feasibility and accuracy of the present method are demonstrated by the numerical evidence of the Stark shifts and widths of H atom ground and excited states. The results agree satisfactorily with the available results in the literature. Moreover, the method provides unambiguous advantages over other existing methods for the calculation of resonance parameters in a many-electron system and is illustrated for the low-lying states of the Li atom under the influence of external DC electric fields. Some new results are reported.

The complex absorbing potential (CAP) method has been applied to compute the complex Stark eigenvalues of low-lying excited states of the hydrogen and the lithium atoms. As a relatively new technique, the method turns out to be a simple and powerful tool for the investigation of resonance parameters in polyelectronic atoms. Results for electric-field effects on the 3s, 3p, 3d, 4s, 4p, 4d and 4f states of Li are presented.

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