ABSG - Gaussian Integration

ABSORPTION CORRECTION TOOLS

Absorption correction based on face indexing and integration on a Gaussian grid.

The modified Coppens code (see Crystallographic Computing, 1970) has been implemented in PLATON and adapted to fit into the direction cosine regime introduced with SHELX-76 (compatible with SHELXL97).

Two files are needed:

1. name.ins : instruction file
   

2. name.hkl : reflection file (h,k,l,F^2,sig(F^2) + direction cosines)
   with SHELXL HKLF 4 format (3I4, 2F8.2,I4,6F8.5).

PLATON/ABSG instruction file format:

TITL text
CELL lamda a b c alpha beta gamma
FACE h k l d
...(etc)...
ABSG mu (nx ny nz)

Notes:

• d is the distance to a choose reference centre inside the crystal

• the dimensions of mu and d should be the same (i.e. mm or cm and their corresponding reciprocals)

• nx, ny & nz are the 'Gauss grid numbers in the x, y & z direction respectively.
  The Gauss numbers can be omitted or set to even numbers (e.g. 8).
  High values (e.g. 32) should give accurate values similar to those obtained with ABST. However, computing time increases rapidly with increasing Gauss number values.

• Analytical integration in place of Gaussian integration can be done by substituting the last instruction by 'ABST mu ',

PLATON/ABSG may be run for name.ins through:

platon name.ins

The corrected data are written to (SHELX HKLF 4 style): name.hkp

See ABST for test data and EXAMPLE DATA.