Advanced x-ray pump-probe spectroscopy of electron-nuclear dynamics in molecules
Title: Advanced x-ray pump-probe spectroscopy of electron-nuclear dynamics in molecules
SNIC Project: SNIC 2022/22-308
Project Type: SNIC Small Compute
Principal Investigator: Victor Kimberg <>
Affiliation: Kungliga Tekniska högskolan
Duration: 2022-03-21 – 2023-04-01
Classification: 10407


Fast development of the x-ray facilities and experimental techniques allows studying the x-ray induced dynamics of complex molecules with ultra-high temporal and spatial resolution using advanced x-ray spectroscopy methods. Growing experimental interest requires already now theoretical simulations on a high accuracy level in order to model complex x-ray processes in free molecules and liquids. Theoretical background for various processes under x-ray excitation, including pump-probe spectroscopy techniques, was initially developed in our group and applied to studies of atoms and molecules. In the present project we plan to use high performance computers at SNIC for highly accurate simulations of the electron-nuclear dynamics of quantum systems with a large number degrees of freedom. The numerical methods proposed in the project combine quantum and classical approaches, when fully quantum description is used for modelling of the nuclear motion, ab initio or DFT methods are used for the electronic structure simulations, and the ab initio molecular dynamics (AIMD) is used for simulation of the local molecular structure in a large molecular cluster simulating liquid system. Sufficient part of the project is devoted to modelling of the nuclear wave packet dynamics in multidimensional space. In the present project we plan to use a well optimized home-made codes eSPec, XRAMP and RAM (VCRAM) developed for the solution of the complex dynamical problems on x-ray transitions. The software was tested on multi-core clusters and successfully applied for studies of small molecular systems. Our method, implemented in eSPec package, combines a time-dependent and stationary description for different degrees of nuclear freedom, allowing to sufficiently improve computational costs. In the present proposal, we will use the developed software for accurate quantum calculations of the real systems (water, methanol, acetic acid, etc.) with practical applications, based on experimental collaborations. One of the main goals of the project is to support the experimental activities of our collaborators from x-ray facilities around the world, with particular focus on high-resolution X-ray spectroscopy VERITAS beamline @ MAX IV (Lund, Sweden), SQS beamline @ The European XFEL and FLASH II (Hamburg, Germany).