Indexing of powder patterns is a key step in structural characterization of an unknown powder sample. Three most popular programs – TREOR, ITO and DICVOL – often fail while dealing with poor patterns containing badly-shaped peaks and/or peaks from unidentified impurities. To help the researcher to overcome these obstacles, the new program GRINDEX (GRid search INDEXing) has been developed. In the search of correct unit cell dimensions using a list of non-ideal peak positions, GRINDEX systematically explores all possible cell parameters within specified limits. For each unit cell being tested, the calculated peak positions are compared with the experimental ones and the solution is selected by the least value of discrepancy R-factor. This is a quite heavy task but it becomes possible at present computer progress level.
GRINDEX has a friendly Windows-based interface and some useful options. It allows specifying expected volume of the asymmetric unit to reduce calculation time and to eliminate definitely erroneous solutions; in this case GRINDEX automatically uses the most frequent Z values for each crystal system. When the crystal structure is expected to be isostructural  to a known structure, the user may specify different limits for all six cell parameters to test only close cells. GRINDEX accepts experimental peak positions values typed directly in its window and reads them from files. Several tests of GRINDEX with real data sets showed its efficiency, it easily indexes data sets which could not be indexed by other programs and it is resistant to the presence of some number of impurity peaks (up to 10%). The calculation time takes from seconds (cubic cell) and minutes (orthorhombic cell) to several hours (triclinic cell).

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