Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

ASTRA: a Transition-Density-Matrix Approach to Molecular Ionization



Luca Argenti, Juan Martín Randazzo, carlos maranthe, Jeppe Olsen, Siddhartha Chattopadhyay, Barry I. Schneider


We describe ASTRA (AttoSecond TRAnsitions), a new close-coupling approach to molecular ionization that uses many-body transition density matrices between ionic states with arbitrary spin and symmetry, in combination with hybrid integrals between Gaussian and numerical orbitals, to efficiently evaluate photoionization observables. Within the TDM approach, the evaluation of interchannel coupling is exact and does not depend on the size of the configuration-interaction space of the ions. Thanks to these two crucial features, ASTRA opens the way to studying highly correlated and comparatively large targets at a manageable computational cost. Here, ASTRA is used to predict the parameters of bound and autoionizing states of the boron atom and of the N2 molecule, as well as the total photoionization cross section of boron, N2 and formaldehyde, H2CO. Our results are in excellent agreement with available theoretical and experimental values from the literature. As a proof of principle of ASTRA's ability to tackle larger targets, we report preliminary results for the photoionization cross section of magnesium-porphyrin (MgH12C20N4), a biologically relevant metallorganic complex with as many as 37 atoms.
Physical Review Research


attosecond spectroscopy, time-dependent Schroedinger equation, molecular photoionization, transition density matrices


Argenti, L. , Randazzo, J. , maranthe, C. , Olsen, J. , Chattopadhyay, S. and Schneider, B. (2023), ASTRA: a Transition-Density-Matrix Approach to Molecular Ionization, Physical Review Research, [online],, (Accessed April 15, 2024)
Created November 3, 2023, Updated March 27, 2024