Molecular Photoionization Cross-Sections By Application Of Stieltjes Imaging To Lanczos Pseudospectra

Stielijes imaging technique is widely used for ab initio computation of photoionization cross-sections and decay widths. The main problem hampering the application of the standard Stieltjes imaging algorithms in conjunction with high-level ab initio methods to polyatomic molecules is the requirement of full diagonalization of excessively large Hamiltonian matrices. Here we show that the full diagonalization bottleneck can be overcome by applying the Stieltjes imaging procedure to Lanczos pseudospectrum of the molecular Hamiltonian. The new technique is applied to calculation of the total photoionization cross-section of benzene within an ab initio approach explicitly taking into account single and double electronic excitations. A good agreement with the experimental cross-section is obtained.