Preparation of data for the DATA routine |
This routine reads the basic crystallographic information like cell parameters, space group symbol (it may be also found by the program, using "findspace" directive), wavelength, unit cell content and the counts (or reflections). It includes a modified version of the subroutine SYMM Burzlaff & Hountas (1982). Symmetry operators are directly derived from the space group symbol.
An external file (containing counts or reflections) is supplied by the user. If an external reflection file is supplied (avoiding the extraction step),diffraction data are checked in order to find out equivalent reflections or systematically absent reflections (which are then excluded from the data set).
ALPHA
It is used to start the alpha2 stripping.
CELL a b c α β γ
cell dimensions a, b, and c are in angstroms, α, β and γ in degrees.
CONTENTS El1 n1 El2 n2 El3 n3 .........
Unit cell contents. Eli is the chemical symbol of atomic species i, ni is the corresponding number of atoms in the unit cell (to a maximum of 8 atomic species). For each chemical element up to Cf (Z=98) X-ray scattering factor constants are stored, together with information on the atomic number and weight, covalent and Van-der-Waals radii, etc. in a file (see notes on implementation). Neutron scattering factors are coded in the program for elements up to Pu (Z=94).
EQUIPORTION
If this directive is given the overall intensity of a group of overlapping reflections is equiportioned among the reflections in the group (equal E-values are obtained).
EXTEFILE string
This directive is used to supply an external file containing 'd' or '2θ' values of peak positions. In the latter case the additional '2-THETA' directive has to be used.
If this directive is used the program will skip the automatic "peaksearch " procedure.
FILETYPE string
This directive is used to specify the format of input file containing the diffraction data. string defines the type of file and can be 'counts', 'xy', 'double', 'gsas'.
If the directive FILETYPE string is absent or string is 'counts' the first three number at the beginning of the counts file must be the 2theta minimum, 2theta step and 2theta maximum. The following lines must be counts. The number of counts for row or the format of counts can vary.
#Example 1: use, in the input file, the directive 'FILETYPE counts' or nothing
7.00 0.020 100.00
3017 2925 3056 2983 3008 2953 2875 2976 2886 2928
2973 2831 2960 2821 2854 2900 2857 2798 2876 2798
2819 2865 2830 2735 2771 2813 2806 2704 2823 2878
2793 2795 2756 2722 2705 2736 2802 2657 2811 2736
2753 2722 2780 2734 2795 2741 2812 2808 2713 2746
2696 2747 2799 2876 2741 2921 2776 2966 3017 3082
3058 3193 3147 3309 3319 3404 3490 3554 3684 3845
4015 4069 4293 4450 4657 4905 5201 5587 5796 6172
6646 7225 7834 8918 9767 10641 11891 13411 15091 17902
....................................................................................................................
#Example 2: use, in the input file, directive 'FILETYPE counts' or nothing
6 0.01 55.98
412.98
404.51
412.40
405.57
403.30
405.94
404.89
389.39
396.55
408.00
403.24
385.44
396.46
393.20
390.52
401.58
.............................................................................................................
If string is 'xy' the counts file contains 2theta in the first column and the intensities in the second one. The format of counts can vary.
#The use of directive 'FILETYPE xy'
4.700 4769.000 69.05795
4.714 4860.000 69.71370
4.729 4794.000 69.23872
4.743 4857.000 69.69218
4.758 4837.000 69.54855
4.772 4891.000 69.93568
4.787 4788.000 69.19537
4.801 4886.000 69.89993
4.816 4720.000 68.70226
4.830 4688.000 68.46897
4.845 4690.000 68.48357
4.859 4867.000 69.76389
4.874 4800.000 69.28204
4.888 4863.000 69.73521
...........................................................................................................................
If string is 'double' the first line in the counts file contains 2theta minimum, 2theta step, 2theta maximum. The rest of file contains intensities and standard deviations on separated lines.
#The use of directive 'FILETYPE double'
3.000 0.005 41.600
3567.2 3405.3 3370.1 3432.4 3476.2 3526.9 3354.7 3596.6 3476.8 3676.7
67.27 65.44 65.16 65.78 66.12 66.55 64.64 67.14 66.08 67.88
3623.0 3703.6 3555.1 3500.3 3558.6 3584.8 3606.2 3556.8 3710.3 3704.8
67.46 68.33 66.89 66.12 66.77 67.00 67.75 66.77 68.73 68.03
3721.0 3670.7 3775.1 3796.4 3820.9 3880.8 3809.1 3922.7 3963.5 3919.6
68.76 67.82 68.60 69.04 69.28 70.05 69.39 69.91 70.44 70.11
4062.6 4104.5 4148.8 4219.5 4221.6 4376.3 4294.3 4439.1 4349.1 4500.5
71.69 71.85 71.87 72.61 72.61 73.94 73.66 74.44 74.18 75.39
4449.2 4704.1 4833.7 4851.3 4892.2 5105.9 5143.3 5161.8 5272.0 5418.5
74.34 77.34 78.13 78.37 78.02 79.82 80.53 80.55 81.09 81.93
5543.3 5635.8 5918.0 6007.9 6406.6 6395.2 6515.0 6753.3 7255.9 7464.6
83.36 84.18 86.37 86.95 89.58 89.58 90.60 91.99 95.62 96.94
7811.5 8415.6 8597.6 9251.3 9995.7 10714.5 11097.2 11067.4 10678.3 9864.0
98.89 102.81 103.75 107.71 111.43 115.71 117.76 117.40 115.54 110.72
.............................................................................................................................
In the previous cases comment records can appear at the beginning of data file if the first character is '#' or '!' or '>'. Examples in directory examples.
'FILETYPE gsas' can be used to read counts files in GSAS standard format with keyword TYPE='STD' and TYPE='ESD'.
FINDSPACE
This directive is used in order to find a possible space group when the cell parameters are known.
FWHM x
This directive supplies the value of x for the overlapping calculation. Two reflections are assumed to be in overlapping if 2θ1 -2θ2 < x * FWHM. Default is x = 0.1.
HISTOGRAM n
n is the number of bars in the histogram for the alpha2 stripping procedure (only if ALPHA directive is used).
ISOTOPE El sf
To modify the value of the neutron scattering factor for element El using the value sf. (It must be used if NEUTRON directive is given).
MOREPEAKS
This directive is used together with the peaksearch directive in order to add more low intensity peaks to the set of peaks already detected via the peaksearch directive.
NEUTRON
This directive is used to specify that neutron radiation has been used.
NOREFINE
This directive is used to skip the cluster refinement step in the peak search procedure.
PATTERN filename
Filename is the name of the profile counts file (up to 40 characters). It is used to change the default. [Default is name.pow where name is defined using the command %STRUCTURE].
RANGE thmin thmax
Only intensities included in the range thmin-thmax will be considered; thmin and thmax are the minimum and maximum 2θ value of the powder pattern respectively.
REF2 string
This directive is used to supply an external reflection file. EXPO reads directly the output provided by any profile fitting program. HKL, FWHM and F**2 must be supplied [default format is (3i4,2f15.4)]. If a comment line is at the beginning of the reflection file, the first character must be '>'. If this directive is used, the directives 'pattern' and 'range' must not be introduced.
SHIFT sx sy sz
Origin shift components if desired by the user. They must be integral multiples of 1/24.
SPACEGROUP string
String is the symbol of the space group, according to International Tables (1974). Blanks are necessary among the terms constituting the space group symbol (see examples at the end of this manual).
SYNCHROTRON
This directive is used to specify that synchrotron radiation has been used.
STEP step_value
You can use this directive to specify that your data were collected at fixed step. This directive is activated when the data file contains two columns (2theta values and intensities) and you are using the directive 'FILETYPE xy'. If you use the directive STEP, the first column is ignored and the program automatically recreates the 2theta values by using step_value for the step and the first 2theta value in the data file.
THCORR x
x is the Δθ0 value that is used to correct by zeropoint shift the set of 2θ peak positions.
The shift value will be egual to 2(n-1)Δθ0, where n is the sequential number of the N-TREOR trial.
If this directive is not introduced the Δθ0 default value is the experimental 2θ step.
2-THETA
This directive is used combined with the EXTEFILE directive to supply to the indexing program N-TREOR09 an external file containing 2θ values of peak positions.
WAVELENGTH w
w is the wavelength (in Angstrom) used to collect the powder pattern.
References |
Burzlaff H. & Hountas A. (1982). J. Appl. Cryst. 15, 464-467.
Created with the Personal Edition of HelpNDoc: Full-featured Help generator