XLENS, a direct methods program based on the modulus sum function: Its application to powder data

XLENS is a traditional direct methods program working exclusively in reciprocal space. The distinctive feature of XLENS is the use of the modulus sum function as target function for the phase refinement. Due to its efficiency, robustness, and no need of weighting schemes, this function is specially well suited for treating powder diffraction data. The mathematical basis as well as the significance of the most important control parameters of the program will be described here. To illustrate how XLENS works, three different examples will be shown. Due to its simplicity, the modulus sum function can be easily combined with real-space filtering procedures to produce even more efficient crystal structure solving strategies. (C) 1999 International Centre for Diffraction Data. [S0885-7156(99)01502-X].