ASTRA, a transition-density-matrix method for attosecond molecular dynamics

The push of ultrashort light sources to and beyond the water window [1], to high intensity [2], and to ever shorter durations has opened the way to the site-specific x-ray-pump x-ray-probe study of electron dynamics in molecules of chemical relevance. Theoretical tools able to quantitatively resolve in time the correlated and entangled character of molecular ionization processes are necessary to guide these experiments. Here we present ASTRA (AttoSecond TRAnsitions), a program based on an innovative approach to the close-coupling method for molecular ionization. ASTRA makes use of high-order transition density matrices between large-scale-CI ionic states with arbitrary symmetry and multiplicity, obtained with an extension of the LUCIA code [3], and on hybrid Gaussian-B-spline integrals [4,5]. These essential features allow ASTRA to reach core-excitation/decay energies, to account for exchange effects exactly, and to scale independently of the size of the parent-ion configuration space. The talk will focus on ASTRA theory, its current applications, and its future directions.

[1] Duris J et al, Nat. Phot. 14, 30 (2020)

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

[3] Olsen J et al, JCP 104, 8007 (1996)

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

[5] Gharibnejad H et al, CPC 263, 107889 (2021)