Calculation of x-ray scattering patterns from nanocrystals at high x-ray intensity

TL;DR

This paper introduces a comprehensive method for simulating x-ray scattering patterns from nanocrystals under intense x-ray pulses, accounting for radiation damage and non-uniform fluence distributions using a hybrid MC-MD-ab initio approach.

Contribution

It develops a novel subdivision-based simulation framework that models the dynamics within nanocrystals exposed to high-intensity x-ray pulses, incorporating spatial beam profiles and damage effects.

Findings

Simulation of diffraction patterns for crystals larger than the beam profile.

Impact of non-uniform fluence on radiation damage distribution.

Validation of the method with different beam profiles.

Abstract

We present a generalized method to describe the x-ray scattering intensity of the Bragg spots in a diffraction pattern from nanocrystals exposed to intense x-ray pulses. Our method involves the subdivision of a crystal into smaller units. In order to calculate the dynamics within every unit we employ a Monte-Carlo (MC)-molecular dynamics (MD)-ab-initio hybrid framework using real space periodic boundary conditions. By combining all the units we simulate the diffraction pattern of a crystal larger than the transverse x-ray beam profile, a situation commonly encountered in femtosecond nanocrystallography experiments with focused x-ray free-electron laser radiation. Radiation damage is not spatially uniform and depends on the fluence associated with each specific region inside the crystal. To investigate the effects of uniform and non-uniform fluence distribution we have used two different spatial beam profiles, gaussian and flattop.