XABS2 - AN EMPIRICAL ABSORPTION CORRECTION PROGRAM

The XABS2 Fortran program calculates an empirical absorption correction based on minimization of the differences between F(obs)2 and F(calc)2. The basic algorithm has been used in the crystallography laboratory at the University of California, Davis for over a decade, in the form of the program XABS. XABS relied upon an approximately linear relationship for spherical crystals between the transmission factor and sin2 theta for theta less-than-or-similar-to 30-degrees when muR less-than-or-similar-to 5. In XABS2, deviations from linearity are accounted for by a cubic equation in sin2 theta, which makes it applicable over the whole range of diffraction angle. The program needs no data in addition to the unique set but assumes a bisecting (symmetric) data-collection mode on a four-circle diffractometer. Since it does not require knowledge of the diffractometer setting angles, it can be applied even in cases where details of the original data collection are unknown.