8.2. STEM simulation

STEM.mp4

The computation time for STEM images depends strongly on the following factors:
- Convergence angle of incident electrons. A larger convergence angle means a larger overlap of diffraction disks. Solving interference between the disks has a high computational cost.
- Number of Bloch waves. To obtain the amplitude of the diffractive waves, we need to solve the eigenvalues/vectors problem for the potential matrix. Its computational cost is proportional to the cube of the number of Bloch waves.
- Angular resolution of incident electrons. ReciPro divides the direction of the convergence electrons and solves the Bloch wave for each direction. Of course, the finer the division, the more accurate it is, but the computation time increases.
Usually, BF and ABF images (detection range is inside the convergence electron angle) are strongly influenced by elastically scattered electrons, while LAADF and HAADF (detection range is outside the convergence electron angle) are influenced by inelastically scattered electrons.
- When calculating inelastic intensities, the temperature factors of the atoms must be set NOT to zero. If you are not sure, set B = 0.5 Å^2 for all atoms.
- The intensity of electrons at large scattering angles such as HAADF is approximately proportional to the square of the atomic number.

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