The thermal diffuse scattering contribution to the absorptive potential in high-energy electron diffraction is calculated in the form of an absorptive contribution to the atomic form factor. To do this, the Einstein model of lattice vibrations is used, with isotropic Debye-Waller factors. The absorptive form factors are calculated as a function of scattering vector s and temperature factor M on a grid which enables polynomial interpolation of the results to be accurate to better than 2% for much of the ranges 0-< Ms 2<-6 and 0_< M_<2/~2. The computed values, together with an interpolation routine, have been incorporated into a Fortran subroutine which calculates both the real and absorptive form factors for 54 atomic species.

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People seldom take absorption very seriously in electron diffraction calculations. Since the work of Hashimoto et al. it has been common practice to set the absorbative part of the potential coefficient V′g to be one tenth of the elastic part Vg. Although this may not be a bad approximation in simple metals, there is no reason why it should apply to more complicated structures. Here, Vg may be small because of interference between different atoms in the unit cell, but the same cancellation might not occur in V′g because the individual atomic contributions to Vg and V′g need not scale in the same way. In fact, the absorbative contribution increases more rapidly with atomic number than the elastic part. This effect is particularly marked in non-centrosymmetric crystals, where V′g and Vg need not have the same phase. Both V′g and Vg are now complex numbers which we write as(1)The squared modulus of the total potential coefficient now becomes(2)If g → −g, ϕ and ϕ′ change sign, so if the phase difference is non-zero the overall magnitude of the +g and −g potential coefficients are not equal. The standard assumption is that |V′g| = 0.1|Vg| and ϕg − ϕ′g = 0, which ignores corrections to the magnitude of Vg of order | V′g/Vg|.