SYMMETRY-FACTOR MAPS: COMPUTING PROGRAMS AND DICHROMATIC SYMMETRY.
SOUTHERN ILLINOIS UNIV CARBONDALE MATERIALS SCIENCE LAB
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The structure-factor is a trigonometrical expression that represents the resultant effect of the wave scattered by the atoms of a unit cell. Crystal-structure analysis is based on finding the best fitting of the atomic coordinates of atoms of a given scattering power to give the best values of the calculated amplitudes in relation to the observed intensities. The form of the trigonometrical expression depends upon the symmetry of the crystal structure that is, it depends on the geometrical distribution of atoms equivalent by symmetry, i.e., the equipoint of an atom in the unit cell. The contribution of an atom in the position x, y, z depends then upon those coordinates and the equipoint determined by the symmetry elements of the space group. Two programs, SFM-symmetry-factor mapping, and SFMPLT - symmetry-factor map plot, have been developed to calculate and plot the function for given combination of h, k. The resulting maps show dichromatic symmetry that is systematically studied. Author
- Computer Programming and Software