Dialog Box: Align Face or Vector [Rotation Menu - Atoms window only]
This will rotate a specified crystal face (hkl) to lie flat in the screen or paper (face-normal parallel to x observer), or a vector (uvw) to be perpendicular to the screen or paper. To align a face, it is also necessary to specify a vector lying in the face which will be vertical in the screen or paper (z direction). Conversely, to align a vector, it is necessary to specify a face, containing the vector, whose normal will be vertical. If a vector [uvw] lies in a face (hkl), the indices satisfy the condition hu + kv + lw = 0.
You can elect to use the default alignment vector or face, instead of specifying it. The default vector will be the intersection of the face (hkl) with the face (100), whose indices are given by the cross product (hkl)x(100). If the face (hkl) is (100), the default alignment vector will be the vector [001]. For aligning a vector the algebra is just the same, with interchange of face and vector.
When dealing with a molecule or polymer, using a Cartesian axial system, this rotation option can be used to obtain a view down a given vector direction. Use the vector alignment option, although when the structure axes are Cartesian the two cases of aligning a face or a vector are identical. After specifying the initial vector or view direction, if you do not accept the default you must then give another vector, in place of the "face indices", which is perpendicular to the first vector, and which is to be vertical (z direction). If the two vectors are at right angles, their coefficients or "indices" multiplied together (the vector dot product) should equal zero as in the above condition for a vector lying in a face.