Calculations of photoionization cross-sections with variationally optimized complex Gaussian-type basis functions

Photoionization cross-sections of various simple systems were calculated with variationally optimizing the complex orbital exponents in Gaussian-type basis functions within the framework of the complex basis function method. The optimizations were performed with the numerical Newton-Raphson method based on the variational principle for the frequency-dependent polarizabilities. Accurate cross-sections were obtained for the Rydberg autoionization of He and Be, and the photodetachment of H^- with the optimizations of only one complex basis function. These results show the effectiveness of the optimization of the complex orbital exponents to reduce the number of basis functions significantly and imply the applicability to general problems by adapting many existing techniques developed in bound state theories.