ASTRA: a scalable wave-function approach to the photoionization of polyatomic molecules*

Ultrafast laser technologies keep extending the intensity and frequency of attosecond pulses [1,2]. In molecules, these pulses excite coherent ionization wavepackets that require a correlated wave-function approach to accurately describe their evolution. We present several ionization observables for diatomic (nitrogen and carbon monoxide) and polyatomic (formaldehyde and ethylene) molecules, computed with the ASTRA suite of codes [3]. ASTRA implements a new approach to the close-coupling representation of the molecular electronic continuum based on high-order transition density matrices (TDM) between correlated ionic states with arbitrary multiplicity, obtained with an extension of LUCIA, a general large-scale configuration-interaction code [4], and on hybrid Gaussian-B-spline integrals [5], where the latter can be extended to reach quantization boxes of hundreds atomic units. Total and partial photoionization cross sections together with photoelectron angular distributions compare well with established benchmarks [6,7]. The efficient spin-string formalism of TDM's algorithms in LUCIA [8] makes ASTRA scale favorably with molecular size, thus opening the way to study correlated dynamics in complex molecules. This work is supported by the DOE CAREER grant No. DE-SC0020311. Part of the calculations used NERSC resources under the contract No. DE-AC02-05CH11231 and the award BES-ERCAP0024720.

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[2] Saito N et al, Optica 6, 1542 (2019)

[3] Randazzo J M et al, arXiv:2211.10316 [physics.atom-ph] (2022).

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

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

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

[8] Olsen J et al, JCP 89, 2185 (1988)