Luca Argenti

University of Central Florida

"From atoms to molecules, theory on the heels of attosecond electron dynamics"

October 27, 2025

Abstract

Attosecond science has been instrumental to resolve in time photoionization processes and coherent electronic excitations in atoms, molecules, and solids. In this context, ab initio time-dependent close-coupling, wave-function based methods are the most effective approaches for accurately describing processes influenced by multiple excitations and by the entanglement between photo fragments. In the first part of the talk, I will illustrate the capabilities of some preeminent attosecond technique such as RABBITT, attosecond transient absorption, and non-collinear four-wave mixing through their applications to atomic systems.

In molecules, significant progress has been made with new codes like XCHEM, tRecX, RMT, and UKRmol+. Yet, challenges remain to achieve scalability with respect to the level of ionic correlation and to the target size, and the accurate description of exchange terms with the photoelectron in the molecular region. In the second part of the talk, I will show how, to tackle these limitations, we developed ASTRA (AttoSecond TRAnsitions), a code suite based on high-order transition density matrices between correlated ionic states with arbitrary multiplicity, and on hybrid Gaussian-B-spline integrals. ASTRA has successfully reproduced total and partial photoionization cross section, photoemission asymmetry parameters, and molecular-frame photoelectron angular distributions for molecules including N2, CO, H2CO, and Pyrazine, in good agreement with existing benchmarks.