One- and two-phonon X-ray cross-section calculations for the molecular crystal hexamethylenetetramine

The two-phonon X-ray scattering from hexamethylenetetramine is calculated, and this is compared with the one-phonon result, here independently recalculated. The details of the calculation procedure are fully described, and possible savings in computation discussed. In a few regions of reciprocal space within the Cu Kα reflecting sphere the two-phonon scattering is larger than the one-phonon scattering. It is therefore essential when making quantitative comparisons with experiment that the two-phonon scattering be considered.