Ab Initio Computation of Rotationally-Averaged Pump-Probe X-ray and Electron Diffraction Signals

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Dynamics

Background:

• Accurate computation of molecular diffraction signals is crucial for understanding molecular dynamics.
• Existing methods may lack fidelity or efficiency for complex systems.

Purpose of the Study:

• To develop a new, efficient algorithm for calculating rotationally averaged elastic molecular diffraction signals.
• To enable high-fidelity analysis of pump-probe diffraction experiments.

Main Methods:

• Developed an algorithm using Becke quadrature grids for high-fidelity charge density representation.
• Employed Williamson and Zewail scattering kernels for interaction computations.
• Implemented the algorithm on a GPU for enhanced computational efficiency.

Main Results:

• The method achieves convergence with small grids (<500 points/atom).
• Demonstrated applicability to molecules with up to a few dozen atoms.
• Compared the new method against the independent atom model (IAM), showing improved accuracy.

Conclusions:

• The new algorithm provides an accurate and efficient approach for molecular diffraction signal computation.
• The method is suitable for analyzing polyatomic molecules in pump-probe experiments.
• Explored potential for detecting electronic transition signatures in diffraction data.