Indexing Crystal Faces
The following describes a method for indexing the faces of a crystal mounted on a Bruker platform goniometer with a ccd area detector and a video camera for viewing the crystal. These instructions assume that the Bruker SMART software is being used.
Obtain an orientation matrix in SMART by using the Crystal > Unit Cell or similar means.
Open up the Video program and turn on any light needed to see the crystal. Begin the screen capture.
Start the routine in SMART to index faces using Crystal > Faces then click <OK> once to start the routine and once again to remove the blank list of crystal faces.
Check if the faces may have common (h k l) values by typing
<CNTL>-F, followed by the (h k l). It is suggested that you check the (1 0 0), (0 1 0), and (0 0 1) faces. If the guessed face or its opposite is a true face of the crystal, the crystal will be positioned so that the face is normal to the view and is parallel with a reference axis on the display of the Video program. When a face is found, record the face indices and the distance to the center of the crystal. This distance is typically half of the distance to the opposite face. If the crystal is centrosymmetric, record the opposite face as well.
When sufficient faces to enclose the general shape have been identified, press <Enter> to get to the list of faces and type in the face indices and distances to the center of the crystal.
Fine tune this list by the method of locating faces above or by moving the image of the crystal in SMART to the position of other faces using the Up, Down, Left, or Right buttons and pressing <END>. The <END> command drives the goniometer to show a face as outlined above. Occasionally you may try to drive the goniometer to a position that may put the instrument in collision. The Faces routine will simply exit with a collision warning. If the list of faces is incomplete, restart the Crystal > Faces routine.
When the list of faces is complete, hit <Esc> to leave the Faces routine. Stop the Video program. Turn out any light used to illuminate the crystal.
Run the Least Squares refinement of the cell parameters at least one more time to save the face information to the *.p4p file.