Breakdown of the dipole approximation in core losses

The validity of the dipole approximations commonly used in the inelastic scattering theory for transmission electron microscopy is reviewed. Both experimental and numerical arguments are presented, emphasizing that the dipole approximations cause significant errors of the order of up to 25% even at small momentum transfer. This behavior is attributed mainly to non-linear contributions to the dynamic form factor due to the overlap of wave functions. -- Highlights: → Breakdown of the dipole approximation at small scattering angles. → Wavefunction information available in double differential scattering cross section. → Angle-resolved Wien2k simulations agree well with experimental data.