title: Total molecular photoionization cross-sections by algebraic diagrammatic construction-Stieltjes-Lanczos method: benchmark calculations.
abstract: In [K. Gokhberg, V. Vysotskiy, L. S. Cederbaum, L. Storchi, F. Tarantelli, and V. Averbukh, J. Chem. Phys. 130, 064104 (2009)] we introduced a new L(2) ab initio method for the calculation of total molecular photoionization cross-sections. The method is based on the ab initio description of discretized photoionized molecular states within the many-electron Green's function approach, known as algebraic diagrammatic construction (ADC), and on the application of Stieltjes-Chebyshev moment theory to Lanczos pseudospectra of the ADC electronic Hamiltonian. Here we establish the accuracy of the new technique by comparing the ADC-Lanczos-Stieltjes cross-sections in the valence ionization region to the experimental ones for a series of eight molecules of first row elements: HF, NH3, H2O, CO2, H2CO, CH4, C2H2, and C2H4. We find that the use of the second-order ADC technique [ADC(2)] that includes double electronic excitations leads to a substantial systematic improvement over the first-order method [ADC(1)] and to a good agreement with experiment for photon energies below 80 eV. The use of extended second-order ADC theory [ADC(2)x] leads to a smaller further improvement. Above 80 eV photon energy all three methods lead to significant deviations from the experimental values which we attribute to the use of Gaussian single-electron bases. Our calculations show that the ADC(2)-Lanczos-Stieltjes technique is a reliable and efficient ab initio tool for theoretical prediction of total molecular photo-ionization cross-sections in the valence region.
authors.affiliation: Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Ruberti
authors.forename: R
authors.initials: R
authors.lastname: Yun
authors.forename: K
authors.initials: K
authors.lastname: Gokhberg
authors.forename: S
authors.initials: S
authors.lastname: Kopelke
authors.forename: L S
authors.initials: LS
authors.lastname: Cederbaum
authors.forename: F
authors.initials: F
authors.lastname: Tarantelli
authors.forename: V
authors.initials: V
authors.lastname: Averbukh