Numerical simulation of the resonant forbidden bragg reflection in germanium

“Forbidden” reflections are observed in synchrotron radiation diffraction when the energy of incident radiation is close to the absorption edges in crystals. In the present paper, a new method for calculating the intensity of thermal-motion-induced forbidden reflections is proposed. It includes two steps: simulation of the temporary atomic displacements with the help of the ab initio molecular dynamics followed by quantum-mechanical calculations of the resonant scattering amplitude for various configurations. This technique is applied to the calculation of the 600 reflection thermal behavior in Ge and gives an adequate quantitative fitting of experimental data. The proposed simulation method of the thermal-motion-induced forbidden reflections is suitable for any crystal structure and promises to explain many results obtained up to now in synchrotrons.