The indexing directives

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The indexing directives

Directives in data command

The following directives must be added after the command '%data' in the input file to activate some specific features of the indexing procedure

EXTEFILE file_name

This directive is used to supply an external file containing 'd' or '2theta' values of peak positions. In the latter case the additional '2-THETA' directive has to be used. This directive is used in place of the peaksearch directive. An example of the use of the directive extefile for the indexing of the pattern of structure bamo:

%job bamo - home diffractometer data
%structure bamo
%initialize
%data
pattern bamo.pow
wavelength 1.5406
extefile bamo.pea
%ntreor
%continue

'bamo.pea' is an ASCII file containing the observed 'd' values associated to the selected peaks.

2-THETA

This directive is used combined with the EXTEFILE directive to supply to the indexing program N-TREOR09 an external file containing 2theta values of peak positions.


Directives in ntreor command

The N-TREOR09 directives must be added after the command '%ntreor' in the input file to enable some specific features of the indexing procedure

All the directives of the indexing program TREOR (Werner, Eriksson & Westdahl, 1985) are still valid for the "%ntreor" command and have to be used with the same syntax (see the N-TREOR manual for the details).

If a set of d (or 2theta) values is already available, the peak search procedure is skipped.

CEM n

%structure diltia
%initialize
%data
pattern pd_0029.pow
wavelength 1.54056
filetype xy
extefile diltia.pea
%ntreor
CEM = 50,
%continue

'diltia.pea' is an ASCII file containing the d peak positions.

The indexing program N-TREOR09 searches for cells with a maximum cell volume of 4000 Å3 and a maximum cell axis of 35 Å. Due to this limit on cell axis the correct cell is not found in a default indexing run for the diltia structure. The default choices can be changed via suitable directives. In particular, the N-TREOR09 directives 'CEM = 50' activate a search for a cell having a maximum axis value of 50 Å.

TREORCELL num1 num2

This directive enables to select for refinement at the N-TREOR run "num2" (among all the N-TREOR runs carried out by EXPO) the cell numbered "num1" [among the possible cell sorted in function of the M'20 figure of merit (Altomare et al., 2000)]. The selected cell will be automatically refined via the program PIRUM (Eriksson & Werner, 1995).

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