HKLF Command

HKLF  n [0]  s [1]  r11...r33 [1 0 0 0 1 0 0 0 1]  wt [1]  m [0]

n = 1:

SHELX-76 condensed data (BN is set to one). 'Condensed data' impose unnecessary index restrictions and can introduce rounding errors; although they still have their uses (email!), SHELXL-93 cannot generate condensed data and their use is discouraged.

n = 2:

h k l F_o² sigma(F_o²) BN [1] lambda [#] in FORMAT(3I4,2F8.2,I4,F8.4) for refinement based on singlet reflections from Laue photographs. The data are assumed to be scaled for source intensity distribution and geometric factors and (if necessary) corrected for absorption. If lambda is zero or absent the value from the CELL instruction is used. n = 2 switches off the merging of equivalent reflections BEFORE l.s. refinement (i.e. sets MERG 0); equivalents and measurements of the same reflections at different wavelengths are merged after least-squares refinement and the subsequent application of a dispersion correction, but before Fourier calculations.

n = 3:

h k l F_o sigma(F_o) BN [1] (if BN is absent or zero it is set to 1). The use of data corresponding to this format is NOT RECOMMENDED, since the generation of F_o and sigma(F_o) from F_o² and sigma(F_o²) is a tricky statistical problem and could introduce bias.

n = 4:

h k l F_o² sigma(F_o²) BN [1] for the standard reflection data file. Since F_o² is obtained as the difference of the experimental peak and background counts, it may be positive or (occasionally) negative.

n = 5:

h k l F_o² sigma(F_o²) m where m is the twin component number. Each measured F_o² value is fitted to the sum of k[|m|]*F_c[|m|]² over all contributing components, multiplied by the overall scale factor. m should be given as positive for the last contributing component and negative for the remaining ones (if any). The values of F_o² and sigma(F_o²) are taken from the last ('prime') reflection in a group, and may simply be set equal for each component, but the indices h,k,l will in general take on different values for each component. The starting values of the twin factors k[2]..k[max(m)] are specified on BASF instruction(s); k[1] is given by one minus the sum of the other twin factors. Note that many simple forms of twinning can also be handled with HKLF 4 and a TWIN instruction to generate the indices of the remaining twin component(s); HKLF 5 is required if the reciprocal space lattices of the components cannot be superimposed exactly. HKLF 5 sets MERG 0.

n = 6:

h k l F_o² sigma(F_o²) m as for n = 5, there may be one or more sets of reflection indices corresponding to a single F_o² value. The last reflection in a group has a positive m value and the previous members of the group have negative m. The values of F_o² and sigma(F_o²) are taken from the last ('prime') reflection in a group, and may simply be set to the same values for the others. m is here the reflection MULTIPLICITY, and is defined as the number of equivalent permutations of the given h, k and l values, not counting Friedel opposites. This is intended for fitting resolved powder data for high symmetry crystal systems. For example, in a powder diagram of a crystal in the higher cubic Laue class (m3m) the reflections 3 0 0 (with multiplicity 3) and 2 2 1 (multiplicity 12) would contribute to the same measured F_o². HKLF 6 sets MERG 0. HKLF 6 may not be used with BASF.

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