Ab initio calculation of inelastic scattering.

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. The results are validated by comparison to analytical cross sections in H and He+, and by comparison to experimental results and previous theory for closed-shell He and Ne atoms, open-shell C and Na atoms, and the N2 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.