MERG Instruction

MERG n [2]

If n is equal to 2 the reflections are sorted and merged before refinement; if the structure is non-centrosymmetric the Friedel opposites are not combined before refinement (necessary distinction from SHELXS). If n is 1 the indices are converted to a 'standard setting' in which l is maximized first, followed by k, and then h; if n is zero, the data are neither sorted nor converted to a standard setting. n = 3 is the same as n = 2 except that Friedel opposites are also merged (this introduces small systematic errors and should only be used for good reason, e.g. to speed up the early stages of a refinement of a light atom structure before performing the final stages with MERG 2). Note that the reflections are always merged, and Friedel opposites combined, before performing Fourier calculations in SHELXL_93 so that the (difference) electron density is correctly scaled. Even with n = 0 the program will change the reflection order within each data block to optimize the vectorization of the structure factor calculations (it is shuffled back into the MERG order for LIST 4 output). Note that MERG may not be used in conjunction with TWIN or HKLF 5 or 6. In SHELX_76, MERG 3 had a totally different meaning, namely the determination of inter-batch scale factors; in SHELXL_93, these may be included in the refinement using the BASF instruction.