Title:	Non-linear x-ray-matter interaction with applications to free-electron laser facilities
DNr:	SNIC 2016/1-77
Project Type:	SNIC Medium Compute
Principal Investigator:	Victor Kimberg <kimberg@kth.se>
Affiliation:	Kungliga Tekniska högskolan
Duration:	2016-03-01 – 2017-03-01
Classification:	10407 10302
Homepage:	http://www.theochem.kth.se/research/xfel.html
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 resolution in non-linear x-ray spectroscopies. Growing experimental interest requires already now theoretical simulations on a high accuracy level in order to model complex nonlinear x-ray processes for XFEL applications. Theoretical background for non-linear processes in x-ray regime was initially developed in our group and applied to studies of non-linear interaction of x-rays with atoms and diatomic 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 polyatomic systems in XFEL pulses taking into account the nonlinear interaction with strong x-ray radiation. The numerical simulations proposed in the project are based on semi-classical approach when propagation of the x-ray pulses is described by classical electrodynamics (Maxwell equations) while the material response is treated on quantum mechanical level employing the density matrix equations. The solution of coupled density matrix and Maxwell equations is very demanding and computationally expensive problem. In the present project we plan to use a well optimized home-made software XRAMP developed for the solution of the coupled equations for molecular targets, which allows including an arbitrary number of the vibrational quantum sublevels of the electronic states participating in non-linear x-ray scattering. The software was tested on multi-core clusters and successfully applied for studies of diatomic molecules in high x-ray field regime directly applicable to XFEL application. Our modeling based on realistic parameters of XFEL light can be used as a feasibility study for rather expensive XFEL experimental proposals. One of the main goals of the project is to support the experimental activities of our collaborators from XFEL facilities at LCLS (Stanford, USA) and FLASH (Hamburg, Germany). Our calculations performed during the last 12 month (project 2015/1-69) resulted in two papers accepted for publication in high-level scientific journals (Structural Dynamics and Scientific Reports), as well as served as a support for LCLS experiment in July 2015 (results to be published soon). Moreover, 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. In the present proposal, we will use the software for balky calculations of the real systems (water, etc.) with practical applications.