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19.4.2.4 Properties of the Principal Axis of Motion

Syntax
                                      [ 1 ]
                                { X } [ 2 ]
         property ::= DYN PAANG { Y } [ 3 ]
                                { Z } [ 4 ]
                                      [ 5 ]
                                      [ 6 ]
                                 [ 1 ]
                                 [ 2 ]
         property ::= DYN PABOND [ 3 ]
                                 [ 4 ]
                                 [ 5 ]
                                 [ 6 ]

Function

These property specifications are used for determining the angles between the principal axes of positional time distribution and the bond joined to each atom. Each atom has associated with it space for 6 times 3 sets of angles. Six is required because each atom may have up to six bonds to neighboring atoms. Three is required for the angle between each principal axis and a bond vector. The six sets of three angles are sorted in ascending order on the magnitude of the angle between the x principal axis and the bond vector. Therefore, to obtain the principal axis bond vector angles, one uses the PAANG property specification. In this specification, 1 specifies the angle between the bond whose direction is closest to the first principal axis. 2 specifies the next closest angle, etc. If the number is omitted, 1 is assumed. X, Y, or Z specify which principal axis angle should be included. To allow one to see how the bond vectors have been sorted, the PABOND property specification may be used. PABOND 1 gives the atom number of the first bond in PAANG collection, PABOND 2 gives the next etc. If the number is omitted, 1 is used. The static atom property NUMBER may be used to assist in the identification of the bonded atoms.