----- header of xpowder.pro extracted on: Wed Mar  5 17:24:00 2008

----- Documentation for /scisoft/xop2.3/src_idl/dabax/xpowder.pro -----

 XPOWDER: X-ray diffraction patterns for powder samples



 This application calculates a  X-ray diffraction pattern for 
 a powder crystal. 

 The application is divided in three panels:
 "Asym Unit", "Unit Cell" and "Reflections"

 The main application is under the third panel "Reflection". The
 first two panels are optional with tools to help the user to 
 load and eventually compute the unit cell. 

 The calculation of the powder pattern is done in the routine
 xpowder_calchkl(), which basically 

 i) loads the information of the 
    unit cell (either fom the "Unit Cell" panel or from a file *.ucell, 
    being this a text ASCII file containing in the first line 
    a b c alpha beta gamma (in Angstroms the lengths, and in deg the
    angles) and then a number of lines, one per atom in the unit cell,
    with Z, occupation number, x, y and z (coordinates in crystal units).

    example: Silicon.ucell:
    5.43070 5.43070 5.43070 90.0000 90.0000 90.0000
    14 1.0 0.0 0.0 0.0
    14 1.0 0.0 0.5 0.5
    14 1.0 0.5 0.0 0.5
    14 1.0 0.5 0.5 0.0
    14 1.0 .25 .25 .25
    14 1.0 .25 .75 .75
    14 1.0 .75 .25 .75
    14 1.0 .75 .75 .25
    

 ii) Calculate all possible reflections (permutations of h k l indices)

 iii) Computes the Structure Factor for each reflection, and the
      intensity (only unpolarized beams are used by now). 
      Reflections with intensity inder a cutoff value (in %) are 
      eliminated (considered forbidden reflections). 

 iv) Classifies and displays results. 

 
 The Panel "Unit Cell" permits to load a unit cell, either from
 a *.ucell file or from the DABAX database. 

 The Panel "Asym Unit" contains tools to compute the unit cell. For
 that, the user must enter the atoms in the Asymmetric Unit, and the 
 symmetry operations to be applied. When the 
 "Compute Atoms in the Unit Cell"  button is pressed, the calculation
 is performed in the following way: every atoms in the asym. unit is
 transformed using all the symmetry operations. The redundant atoms 
 are eliminated (and counted for calculating their multiplicity). 
 Optionally, the operations of the 230 spatial symmetry groups can 
 be load from the SpatialGroups.dat DABAX file. Note that this file
 contains the 230 groups and their names as obtained from: 
 http://www.cryst.ehu.es/   (GENPOS application)

 
 All the application information can be stored in a xpowder input file
 for being restored lately. In addition, the user can create text files
 with information that can be loaded in the table widgets, by tagging
 the inputs in the following way:
 
 For Entering data in the "Asym Unit" panel, tag the inputs 
 in this way (example): 


   <starttext>AUATOMS
            57     0.9840        0.0        0.0        0.0         La
             5        1.0     .19930         .5         .5          B
   <endtext>AUATOMS
   <starttext>AUSYM
    x,y,z
    -x,-y,z
    -x,y,-z
   <endtext>AUSYM

 This file can be reaf using File->Load xpowder input file...

 In the same way, information in the "Unit Cell" panel are tagged as:

 <starttext>UCATOMS
       57.00     0.9840      0.000      0.000      0.000         La
       5.000      1.000     0.1993     0.5000     0.5000          B
       5.000      1.000     0.8007     0.5000     0.5000          B
       5.000      1.000     0.5000     0.1993     0.5000          B
       5.000      1.000     0.5000     0.8007     0.5000          B
       5.000      1.000     0.5000     0.5000     0.1993          B
       5.000      1.000     0.5000     0.5000     0.8007          B
 <endtext>UCATOMS
 <starttext>UCCELL
     4.15271    4.15271    4.15271    90.0000    90.0000    90.0000
 <endtext>UCCELL

 


 Author: Manuel Sanchez del Rio, March 2007

 Modification history:
    2007-05-16 srio@esrf.fr added INFO tag,reference directory


  COPYRIGHT:
 	XPOWDER belongs to XOP package and it is distributed within XOP.
 	PLEASE REFER TO THE XOP COPYRIGHT NOTICE
 
  REFERENCE:
 	Published calculations made with XOP should refer:
 
 	M. Sanchez del Rio and R. J. Dejus 
         "Status of XOP: an x-ray optics software toolkit"
         SPIE Proceedings Vol. 5536 (2004) pp.171-174
 
         http://dx.doi.org/10.1117/12.560903
 
  LAST MODIFICATION: srio@esrf.eu 2008-02-01
 
 


