Inner-shell photoabsorption and photoionisation cross-sections of valence excited states from asymmetric-Lanczos equation-of-motion coupled cluster singles and doubles theory

The asymmetric-Lanczos-based equation-of-motion coupled cluster formalism to compute photoabsorption and photoionisation cross-sections of valence excited states [B.N.C. Tenorio, M.A.C. Nascimento, A.B. Rocha, and S. Coriani, J. Chem. Phys. 151 (18), 184106 (2019). doi:] has been adapted to enable the calculation of photoabsorption and photoionisation spectral signatures from inner-shell electrons of such states. Since excited-state properties depend on both the electronic character of the molecular wavefunction and on the nuclear dynamics, we computed the photoionisation spectra using both ground and excited state optimised geometries. The total cross-section profiles were generated for the first two electronically excited states of water, ammonia, ethylene, and uracil by two different methodologies: an analytic continuation procedure based on the Pade approximants and by the Stieltjes imaging procedure. A comparison with literature results, whenever available, is presented. Remarkable differences were observed between the results of the core-ionisation cross-sections of the valence excited states yielded by the two quadrature approaches, at variance from previous studies on the valence photoionisation cross-sections of ground states and of valence excited states. Their origin remains unclear. [GRAPHICS] .

Automated summary

The study adapted the asymmetric-Lanczos-based equation-of-motion coupled cluster formalism to calculate photoabsorption and photoionisation spectral signatures from inner-shell electrons of valence excited states. Two different methodologies were used to generate total cross-section profiles for the first two electronically excited states of water, ammonia, ethylene, and uracil, showing remarkable differences in core-ionisation cross-section results between the two quadrature approaches.