Ab initio calculation of inelastic scattering

Abstract

Nonresonant inelastic electron and X-ray scattering cross sections for bound-to-bound transitions in atoms and molecules are calculated directly from ab initio electronic wavefunctions. The approach exploits analytical integrals of Gaussian-type functions over the scattering operator, which leads to accurate and efficient calculations. Ne atoms, open-shell C and Na atoms, and the N 2 molecule, with both inner-shell and valence electronic transitions considered. The method is appropriate for use in conjunction with quantum molecular dynamics simulations and for the analysis of new ultrafast X-ray scattering experiments.

Theory of ultrafast x-ray scattering by molecules in the gas phase

“…We also note that ultrafast electron diffraction is a closely related experimental technique, both in terms of observables 74,75 and the physical nature of the scattering process. 56,76 Unsurprisingly, for sufficiently coherent electron beams, directly analogous effects to the coherent mixed component described in the current paper appear. 77,78 The theory presented in this paper provides a conceptual framework that can be used to analyze existing and future time-resolved non-resonant x-ray scattering experiments.…”

“…From these two electronic states, all diagonal one-and two-electron scattering matrix elements are computed using our own scattering codes 30,56,57 . The evaluation of the twoelectron scattering matrix elements is based on the work of Wang and Smith 58 , but does not involve the spherical average.…”

Excited Electronic States in Total Isotropic Scattering from Molecules

“…It follows that the theoretical tools devel-oped for and successfully applied in x-ray crystallography for more than a century are not always best suited for ultrafast x-ray scattering. [14][15][16][17][18][19][20][21][22][23][24] Indeed, gas-phase scattering from ground state molecules initially, and, more recently, ultrafast xray scattering, have prompted the development of a number of algorithms that aim the accurate prediction of x-ray scattering starting directly from the ab initio electronic structure of molecules. As gas-phase samples in thermal equilibrium are isotropic, a central question in these methodologies is that of rotational averaging.…”

Ab Initio Calculation of Total X-ray Scattering from Molecules

“…In the following, we outline a method for the calculation of total scattering from ab-initio electronic wavefunctions, based on our previously developed code for the prediction of elastic [30][31][32] and inelastic 33 scattering a . The elastic scattering calculations in particular can be seen as a continuation of pioneering work by Techert and cola Interestingly, the coherence and short pulse duration of XFELs can lead to interference effects involving inelastic scattering matrix elements when scattering from coherent wavepackets is considered.…”