Advanced x-ray spectroscopies for electronic and nuclear dynamics in free molecules and liquids
Title: Advanced x-ray spectroscopies for electronic and nuclear dynamics in free molecules and liquids
DNr: SNIC 2019/3-147
Project Type: SNIC Medium Compute
Principal Investigator: Victor Kimberg <kimberg@kth.se>
Affiliation: Kungliga Tekniska högskolan
Duration: 2019-04-01 – 2020-04-01
Classification: 10407 10302
Homepage: https://www.kth.se/profile/kimberg/page/research-activities
Keywords:

Abstract

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 disordered systems, like 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 take an advantage of high performance computers at SNIC in order to make a qualitative jump to highly accurate simulations of the electron-nuclear dynamics of complex disordered systems with large number degrees of freedom. The numerical simulations proposed in the project are based on hybrid quantum classical approach, 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 (MD) 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 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. 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). Our calculations performed during the last 12 month (project 2018/3-104) resulted in in several papers, including high impact factor journals in our research field, like Nature Communications, PNAS and PCCP [Niskanen, J., PNAS 116, 4058 (2019); Vaz da Cruz, V., Nat. Commun. 10, 1013 (2019); Vaz da Cruz, V., Phys. Rev. A 98, 12507 (2018); Ertan, E., PCCP 20, 14384 (2018)]. In the framework of the project software allowing for 2 and 3 dimensional systems in strong x-rays was developed and tested on SNIC computers, including parallel version. Furthermore, we developed the protocol for mixed quantum-classical simulations on liquids and tested it. 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.