SFAC Instruction
SFAC label a1 b1 a2 b2 a3 b3 a4 b4 c f' f" mu r wt
Scattering factor in the form of an exponential series, followed by real and
imaginary dispersion terms, linear absorption coefficient, covalent radius and
atomic weight. Except for the 'label' and atomic weight the format is the
same as that used in SHELX_76. label consists of up to 4 characters beginning
with a letter (e.g. Ca2+) and should be included before a1; the first label
character may be a '$', but this would be ignored (note however that the '$',
if used, counts as one of the four characters). The two SFAC formats may be
used in the same '.ins' file; the order of the SFAC instructions (and the
order of element names in the first type of SFAC instruction) define the
scattering factor numbers which are referenced by atom instructions. The
units of mu should be barns/atom, as in Table 4.2.4.2 of International Tables,
Volume C (see above).