Abstract
Femtosecond x-ray and electron diffraction hold promise to image the evolving structures of single molecules. We present a unified quantum-electrodynamical formulation of diffraction signals, based on the exact many-body nuclear + electronic wavefunction that can be extracted from quantum chemistry simulations. This gives a framework for analyzing various approximate molecular dynamics simulations. We show that the complete description of ultrafast diffraction signals contains interesting contributions involving mixed elastic and inelastic scattered photons that are usually masked by other larger contributions and are neglected. These terms include overlaps of nuclear wavepackets between different electronic states that provide an electronic decoherence mechanism and are important for the time-resolved imaging of conical intersections.
Highlights
INTRODUCTIONX-ray and electron diffraction signals have become the main tool for exploring the structure of matter.[2]
Over the past century, x-ray and electron diffraction signals have become the main tool for exploring the structure of matter.[2]
We present a unified quantum-electrodynamical formulation of diffraction signals, based on the exact many-body nuclear þ electronic wavefunction that can be extracted from quantum chemistry simulations
Summary
X-ray and electron diffraction signals have become the main tool for exploring the structure of matter.[2]. Contributions that mix diagonal and off diagonal matrix elements of the charge density are highlighted These involve nuclear wavepackets in different electronic surfaces and are of importance in the study of decoherence effects in conical intersection. The electronic and nuclear charge densities are single-body operators in their respective subspaces but many-body effects enter through the many-body wavefunction used to compute their matrix elements. We show that such contributions can in principle be extracted by the separate detection of elastic, inelastic, and non-frequency resolved terms. The terms often missed in XRD (mixed terms of diagonal and off diagonal electronic charge densities) enter in UED through mixed nuclear-electronic charge densities (diagonal nuclear and off diagonal electronic densities)
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