Nuclear Dynamical Correlation Effects in X-ray Spectroscopy from a Theoretical Time-Domain Perspective

Area of Science:

• Physical Chemistry
• Atomic and Molecular Physics
• Computational Chemistry

Background:

• X-ray spectroscopy is a standard technique for probing local electronic structure in complex systems.
• Understanding nuclear dynamics is crucial for accurately interpreting X-ray spectral data.
• Previous methods often overlook or approximate the impact of nuclear motion on spectral features.

Purpose of the Study:

• To develop and validate a rigorous time-correlation function method for analyzing nuclear dynamical correlation effects in X-ray spectra.
• To investigate the influence of nuclear motions on different types of X-ray spectroscopies, particularly resonant inelastic scattering.
• To provide a general methodology applicable across various electronic structure calculations and X-ray techniques.

Main Methods:

• Employed ground-state classical molecular dynamics (MD) simulations to generate nuclear trajectories.
• Developed a time-correlation function approach to explicitly include nuclear dynamical effects.
• Compared results with a conventional sampling approach using the same dataset (gas-phase water).

Main Results:

• The time-correlation function method accurately captures nuclear dynamical correlation effects.
• Second-order resonant inelastic X-ray scattering (RIXS) spectra show significant sensitivity to nuclear motions, unlike first-order absorption.
• The method demonstrates its effectiveness and generality on gas-phase water, highlighting nuclear motion fingerprints in RIXS.

Conclusions:

• Nuclear dynamical correlations play a significant role in interpreting X-ray spectra, especially for inelastic processes.
• The developed time-correlation function method provides a rigorous and general framework for including these effects.
• This methodology can be extended to other X-ray techniques like X-ray photoelectron spectroscopy (XPS) and Auger spectroscopy.