The software package PPXA (programs for precise X‐ray analysis) is described, which provides crystallographers with increased precision and reliability of the results of X‐ray analysis. The package includes programs for: testing the quality of an automatic four‐circle X‐ray diffractometer before X‐ray experiments; optimization of X‐ray diffraction experiments; preliminary processing of experimental data; precise structure analysis up to electron density distribution. The programs for diffractometer testing allow the experimenter to check the stability and precision of the instrument, the homogeneity of the X‐ray beam and the detector sensitivity. The programs for preliminary data processing include: corrections for absorption, taking into account the intensity distribution in the X‐ray beam cross section; correction or elimination of the simultaneous reflection effect; background subtraction, correcting the effects of the scan‐interval cut‐off; correction for thermal diffuse scattering (TDS) for crystals in cases of both known and unknown elasticity constants. The programs for precise crystal structure refinement include options for the determination of primary‐ and secondary‐extinction parameters, atomic coordinates, thermal‐vibration parameters in harmonic and anharmonic approximations, occupation of atomic positions, atom‐core and valence‐shell occupation parameters. The programs were written for a MicroVAX‐II computer with a VAX/VMS operating system and designed to work with CAD‐4 diffractometers and the SDP‐Plus software package. A suitable dialogue with a menu system and detailed user's instructions are available.

No abstract

No abstract

No abstract

The results of intensity profile analysis of Bragg reflections are used for the calculation of the reflectivity Q(Δθij, σij) = W(Δθij, σij)(|F|2Lp)ij in the energy transfer equation for multiwave X‐ray diffraction in crystals. The diffraction profiles in the profile analysis are fitted by different analytical functions and the fitting results are used for modelling the multiwave diffraction. The results of modelling multiwave diffraction in Si and V3Si crystals with different grades of perfection demonstrate that the method suggested here is sensitive to the content of defects in crystals and can be used not only for simultaneous reflection correction in X‐ray structure analysis but also for estimation of single‐crystal perfection.