Revise Structure Fragment
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Dialog Box - called from: Multiple Structures dialog

This gives the start and end numbers of the atoms for the current fragment or individual structure - the atoms are all kept in the same master list. The coordinates, colors, etc. of individual atoms are revised through the Input Atoms dialog in the Input1 menu. The displacement of the current fragment is given in both Cartesian coordinates and coordinates on the structure axes of the current fragment, and the fragment may be moved on either set of axes with the Translate button. The center point, used for rotations, is given in Cartesian coordinates with respect to the zero or center point of the aggregate.

The structure which is in memory when you first add a second fragment provides the overall zero point for translations of individual fragments, and for rotations of the aggregate with the Rotation menu or the on-screen rotations in the Display menu. However, it is possible to rotate the initial fragment, translate it or reset its center point with the subdialogs under Multiple Structures so that its center point and/or orientation are not the same as that of the aggregate.

There are three main types of coordinate system involved in Multiple Structures dialog:

(1) Fixed or reference Cartesian coordinate systems. These apply to all structures and have fixed orientations. The main observer or reference system has a simple relationship to the screen or paper. When Clinographic Viewing is in effect, rotations can also be done on the Clinographic axial system, which is another Cartesian system rotated by a fixed amount relative to the reference system (see Coordinate Systems).

(2) The aggregate or overall structure axes coordinate system. This is taken originally from the first or main structure, but if the first structure is individually translated or rotated through sub-dialogs in Multiple Structures dialog, it may not be the same. Operations in the Rotation menu apply to this coordinate system.

(3) A structure-axes coordinate system for each individual structure. Translations and rotations done with sub-dialogs in Multiple Structures dialog may use these coordinate systems.

Only one set of crystal faces is allowed, and it belongs to the overall structure axes coordinate system. Thus it is possible to rotate the first structure out of proper orientation with the faces. For this and other reasons, rotating structure fragment number 1 individually is not usually advisable.