Treor 90

This is a general trial-and-error indexing program for X-Ray diffraction powder patterns. (i.e. all symmetries included) Trial and error program for indexing of unknown powder patterns cubic-tetragonal-hexagonal-orthorhombic-monoclinic-triclinic symm.

• Dominant zone test is added for the orthorhombic symmetry.
• Dominant zone test is added for the triclinic symmetry.
• Higher order lines among the first seven lines (used in the base line sets) are automatically excluded from the trial phase of the calculations.
• If a monoclinic or triclinic solution is found the program will end with a unit cell reduction followed by a conversion of the reduced cell to a conventional cell according to the metric symmetry. The reduction should be valid unless systematic extinctions are found in the trial cell.
• If a satisfactory solution is found, only the condensed output file is needed. It contains all relevant information and only one indexed list.
• The general output list (that is normally not needed, cf. 5) will only list trials where M20 (or Mxx if less lines are available) is 6 or more and not more than 3 lines among the first 20 (or xx) lines are unindexed.
• If the keyword VOL is given with a negative sign all symmetries are tested until a final solution is found (--if possible). This option should only be used on fast computers. It should NOT be used on a PC (cf. 13 below).
• An algoritm for successive reduction of trial-cell volumes is used in monoclinic and triclinic tests if a negative VOL is given. It is based on the input cell volume limit and the number of trial cells found with IQ (see keyword IQ) or more than IQ indexable lines.
• It is strongly recommended to give only the first (well checked and accurately measured) 25 lines in the diffraction data list (See LINE SET TWO ).
• It is expected that more than 95 per cent of monoclinic and higher symmetry patterns and probably more than 50 per cent of triclinic patterns will be indexed presupposed the data quality is high (i.e. average differences between calculated and observed diffraction angles less than 0.02 deg. and also the weak lines included in the data). The experience of triclinic patterns is limited however.
• Obs. It is important to check cubic, tetragonal and hexagonal solutions by a second run with KS=0 and THS=0 (See key-word list.) Do not trust cubic, tetragonal or hexagonal solutions without an orthorhombic test.
• The reason for testing the symmetries in correct order (from cubic to triclinic) and to START the orthrhombic, monoclinic and triclinic tests with dominant zone tests is that by this procedure false solutions are effectively avoided.
• Vectorization of the subroutines ORTAL, MAEG and COUNT is essential in order to reduce the computing times on a CONVEX 210. For a normal run on CONVEX only the keywords

  CHOICE=X, (see key-word list) and
  VOL=-2000,
  END*
  should be given after the diffraction data list. Computing times of more than 1 minute is rare for monoclinic or higher symmetries. Computing times of more than 5 minutes for a triclinic pattern has not yet been found. For a VAX computing times may be more than 50 times longer. The source code for VAX is not exactly the same as for CONVEX.
• The input format for LINE SET TWO (see below) is changed in agreement with the output format of the diffraction data file from the Guinier-Hagg film scanner program SCANPI (at Stockholm University). The change is mainly of interest for output print of intensities.
• The original Key-word instructions given below are relevant as long as a positive VOL parameter is given.
• If VOL is given a negative value (see 13 above) the following key-words are fixed: MONO=135 and MONOSET=7. Other key-words may be used as in the description below.
• On the output lists M-TEST= xx UNINDEXED IN THE TEST= y usually means that xx is identical with M(20) and y is the number of unindexed lines whithin the first 20 lines (i.e. used for the
  MERIT test). If less than 20 lines are available xx and y refer to the number of lines used.