Correlation effects in molecular ionization with ASTRA, a transition-density-matrix approach to close coupling

XUV and soft-x-ray ultrafast technologies continue extending attosecond-pulse to shorter durations, larger intensities and larger energies [1,2]. The correlated and entangled character of the ionization states obtained with such pulses requires a wave-function approach to describe coherent superpositions of multiple photoelectron-photoion pairs. We present ionization observables for the nitrogen and formaldehyde molecules computed with the ASTRA code (AttoSecond TRAnsitions). ASTRA implements a new approach to the close-coupling representation of the electronic continuum based on high-order transition density matrices between correlated ionic states, obtained with an extension of LUCIA [3], and on hybrid Gaussian-B-spline integrals [4]. Thanks to this approach, ASTRA scale favorably with the molecular size. Resonant photoionization cross sections and photoelectron angular distributions compare well with theoretical and experimental results in the literature (e.g. [5,6]), paving the way to the applications of ASTRA to more complex molecules.

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[4] Masin Z et al, CPC 249, 107092 (2020)

[5] Klinker M et al, JPCL 9, 756 (2018)

[6] Cacelli I et al, CPC 347, 261 (2001)